DISEASES OF THE HORSE'S FOOT
By
H. CAULTON REEKS
Fellow of the Royal College of Veterinary Surgeons Author of 'The Common Colics of the Horse'
1906
To
J. MacQueen, F.R.C.V.S.,
Professor of Surgery at the Royal Veterinary College, London, as a slight acknowledgment of his ability as a teacher, and in return for many kindly services, this volume is gratefully inscribed by
THE AUTHOR.
PREFACE
Stimulated by the reception accorded my 'Common Colics of the Horse,' both in this country and in America, and assured by my publishers that a work on diseases of the foot was needed, I have been led to give to the veterinary profession the present volume.
While keeping the size of the book within reasonable limits, no effort has been spared to render it as complete as possible. This has only been achieved by adding to my own experience a great deal of the work of others. To mention individually those who have given me permission to use their writings would be too long a matter here. In every case, however, where the quotation is of any length, the source of my information is given, either in the text or in an accompanying footnote. A few there are who will, perhaps, find themselves quoted without my having first obtained their permission to do so. They, with the others, will, I am sure, accept my hearty thanks.
The publishers have been generous in the matter of illustrations and diagrams, and although to the older practitioner some of these may appear superfluous, it is hoped they will serve to render the work an acceptable textbook for the student.
H. CAULTON REEKS.
SPALDING, January, 1906.
CONTENTS
CHAPTER I
INTRODUCTION
CHAPTER II
REGIONAL ANATOMY
A. The Bones
B. The Ligaments
C. The Tendons
D. The Arteries
E. The Veins
F. The Nerves
G. The Complementary Apparatus of the Os Pedis
H. The Keratogenous Membrane
I. The Hoof
CHAPTER III
GENERAL PHYSIOLOGICAL AND ANATOMICAL OBSERVATIONS
A. Development of the Hoof
B. Chemical Properties and Histology of Horn
C. Expansion and Contraction of the Hoof
D. The Functions of the Lateral Cartilages
E. Growth of the Hoof
CHAPTER IV
METHOD OF EXAMINING THE FOOT
CHAPTER V
GENERAL REMARKS ON OPERATIONS ON THE FOOT
A. Methods of Restraint
B. Instruments required
C. The Application of Dressings
D. Plantar Neurectomy
History of the Operation
Preparation of the Subject
The Operation
After-treatment
E. Median Neurectomy
F. Length of Rest after Neurectomy
G. Sequelæ of Neurectomy
Liability of Pricked Foot going undetected
Loss of Tone in the Non-sensitive Area
Gelatinous Degeneration
Chronic Oedema of the Leg
Persistent Pruritus
Fracture of the Bones
Neuroma
Reunion of the Divided Nerve
The Existence of an Adventitious Nerve-supply
Stumbling
H. Advantages of the Operation
I. The Use of the Horse that has undergone Neurectomy
CHAPTER VI
FAULTY CONFORMATION
A. Weak Heels
B. Contracted Foot
(a) Contracted Heels
(b) Local or Coronary Contraction
C. Flat-foot
D. Pumiced-foot, Dropped Sole, or Convex Sole
E. 'Ringed' or 'Ribbed' Hoof
F. The Hoof with Bad Horn
(a) The Brittle Hoof
(b) The Spongy Hoof
G. Club-Foot
H. The Crooked Foot
(a) The Foot with Unequal Sides
(b) The Curved Hoof
CHAPTER VII
DISEASES ARISING FROM FAULTY CONFORMATION
A. Sand-crack
Definition
Classification
Causes
Complications
Treatment
Surgical Shoeing for Sand-crack
B. Corns
Definition
Classification
Causes
Pathological Anatomy and Histology
Treatment
Surgical Shoeing for Corn
C. Chronic Bruised Sole
CHAPTER VIII
WOUNDS OF THE KERATOGENOUS MEMBRANE
A. Nail-bound
Definition
Causes
Symptoms
Treatment
B. Punctured Foot
Definition
Causes
Common Situations of the Wound
Classification
Symptoms and Diagnosis
Complications
Prognosis
Treatment
C. Coronitis (Simple)
1. Acute
Definition
Causes
Symptoms
Complications
Prognosis
Treatment
2. Chronic
Definition
Causes
Symptoms
Treatment
D. False Quarter
Definition
Causes
Treatment
E. Accidental Tearing off of the Entire Hoof
CHAPTER IX
INFLAMMATORY AFFECTIONS OF THE KERATOGENOUS APPARATUS
A. ACUTE
Acute Laminitis
Definition
Causes
Symptoms
Pathological Anatomy
Complications
Diagnosis and Prognosis
Treatment
Broad's Treatment for Laminitis
Smith's Operation for Laminitis
B. CHRONIC
1. Chronic Laminitis
Definition
Causes
Symptoms
Pathological Anatomy
Treatment
2. Seedy-Toe
Definition
Causes
Symptoms
Treatment
3. Keraphyllocele
Definition
Causes
Symptoms
Treatment
4. Keratoma
5. Thrush
Definition
Causes
Symptoms
Treatment
6. Canker
Definition
Causes, Predisposing and Exciting
Symptoms and Pathological Anatomy
Differential Diagnosis and Prognosis
Treatment
Malcolm's, Lieutenant Rose's, Bermbach's, Hoffmann's
and Imminger's Treatment for Canker
7. Specific Coronitis
Definition
Causes
Symptoms
Treatment
CHAPTER X
DISEASES OF THE LATERAL CARTILAGES
A. Wounds of the Cartilages
B. Quittor
Definition
Classification
1. Simple or Cutaneous Quittor
Definition
Causes
Symptoms
Pathological Anatomy
Prognosis
Complications
Treatment, Preventive and Curative
2. Sub-horny Quittor
Definition
Causes
Symptoms and Diagnosis
Complications
Necrosis of the Lateral Cartilage
Pathological Anatomy of the Diseased Cartilage
Necrosis of Tendon and of Ligament
Ossification of the Cartilage
Treatment
Operations for Extirpation of the Cartilage
C. Ossification of the Lateral Cartilages (Side-bones)
Definition
Symptoms and Diagnosis
Causes
Treatment
Smith's Operation for Ossification of the Lateral Cartilages
CHAPTER XI
DISEASES OF THE BONES
A. Periostitis and Ostitis
1. Periostitis
(a) Simple Acute Periostitis
(b) Suppurative Periostitis
(c) Osteoplastic Periostitis
2. Ostitis
(a) Rarefying Ostitis
(b) Osteoplastic Ostitis
(c) Caries and Necrosis
Treatment of Periostitis
Recorded Cases of Periostitis
B. Pyramidal Disease, Buttress Foot, or Low Ringbone
Definition
Symptoms and Diagnosis
Pathological Anatomy
Treatment
Recorded Cases of Buttress Foot
C. Fractures of the Bones
1. Fractures of the Os Coronæ
Recorded Cases of Fractures of the Os Coronæ
2. Fractures of the Os Pedis
Recorded Cases of Fractures of the Os Pedis
3. Fractures of the Navicular Bone Recorded Case of Fracture of the Navicular Bone
Treatment of Fractures of the Bones of the Foot
CHAPTER XII
DISEASES OF THE JOINTS
A. Synovitis
(a) Simple
(1) Acute
(2) Chronic
(b) Purulent or Suppurative
B. Arthritis
(a) Simple or Serous
(b) Acute
(c) Purulent or Suppurative
(d) Anchylosis
C. Navicular Disease
Definition
History
Pathology
Changes in the Bursa
Changes in the Cartilage
Changes in the Tendon
Changes in the Bone
Causes
Heredity
Compression
Concussion
A Weak Navicular Bone
An Irregular Blood-supply to the Bone
Senile Decay
Symptoms and Diagnosis
Differential Diagnosis
Prognosis
Treatment
D. Dislocations
LIST OF ILLUSTRATIONS
1. The Bones of the Phalanx 2. The Os Coronæ (Anterior View) 3. The Os Coronæ (Posterior View) 4. The Os Pedis (Postero-lateral View) 5. The Os Pedis (viewed from Below) 6. The Navicular Bone (viewed from Below) 7. The Navicular Bone (viewed from Above) 8. Ligaments of the First and Second Interphalangeal Articulations (Lateral View). (After Dollar and Wheatley) 9. Ligaments of the First and Second Interphalangeal Articulations (viewed from Behind). (After Dollar and Wheatley) 10. The Flexor Tendons and the Extensor Pedis. (After Haübner) 11. The Flexor Perforans and Perforatus 12. The Flexor Perforans and Perforatus (the Perforans cut through and deflected) 13. Median Section of Normal Foot 14. The Arteries of the Foot 15. The Veins and Nerves of the Foot 16. The Lateral Cartilage 17. The Keratogenous Membrane (viewed from the Side) 18. The Keratogenous Membrane (viewed from Below) 19. The Wall of the Hoof 20. Internal Features of the Hoof 21. Inferior Aspect of the Hoof 22. Hoof with the Sensitive Structures removed 23. Section of Epidermis 24. Section of Skin with Hair Follicle and Hair 25. Section of Human Nail and Nail-bed 26. Section of Foot of Equine Foetus. (Mettam) 27. Section from Foot of Sheep Embryo. (Mettam) 28. Section from Foot of Calf Embryo. (Mettam) 29. Section from Foot of Equine Foetus. (Mettam) 30. Section through Hoof and Soft Tissues of a Foal at Term. (Mettam) 31. Perpendicular Section of Horn of Wall 32. Horizontal Section of Horn of Wall 33. Horizontal Section through the Junction of the Wall with the Sole 34. Section of Frog. (Mettam) 35. Professor Lungwitz's Apparatus for Examining the Foot Movements 36. Professor Lungwitz's Apparatus for Examining the Foot Movements 37. The Movements of the Solar and Coronary Edges of the Hoof illustrated. (Lungwitz) 38. The Blind 39. The Side-line 40. Method of securing the Hind-foot with the Side-line 41. The Hind-foot secured with the Side-line 42. The Casting Hobbles 43. Method of securing the Hind-leg upon the Fore 44. The Hind-leg secured upon the Fore 45. The Drawing-knife (Ordinary Pattern) 46. Modern Forms of Drawing-knives 47. Symes's Knife 48-51. Illustrating Colonel Nunn's Method of applying a Poultice to the Foot 52. Poultice-boot of Canvas and Steel 53. Poultice-boot of Cocoa-fibre 54. Foot-swab 55. The Shoe with Plates 56. Quittor Syringe 57. The Esmarch Bandage and Tourniquet 58. Tourniquet with Wooden Block 59. Neurectomy Bistoury 60. Neurectomy Needle 61. Double Neurectomy Tenaculum 62. Adventitious Nerve-supply to Foot. (Sessions) 63. Tip Shoe 64. The Tip Shoe 'let in' to the Foot 65. The Thinned Tip 66. Drawing-knife for Charlier Shoeing 67. The Foot prepared for the Charlier Shoe 68. Bar Shoe 69. Rubber Bar Pad on Leather 70. The Bar Pad applied with a Half-shoe 71. Frog Pad 72. Frog Pad applied 73. Smith's Expansion Shoe for Contracted Feet 74. A Contracted Foot treated with Smith's Shoe 75. De Fay's Vice 76. Hartmann's Expanding Shoe 77. Broué's Slipper Shoe. (Gutenacker) 78. Einsiedel's Slipper and Bar-clip Shoe. (Gutenacker) 79. Hoof showing Coronary Contraction. (Gutenacker) 80. Flat-foot (Solar Surface). (Gutenacker) 81. Hoof showing Laminitis Rings on the Wall. (Gutenacker) 82. Hoof showing 'Grass' Rings on the Wall. (Gutenacker) 83. Club-foot. (Gutenacker) 84. Shoe with extended Toe-piece. (Gutenacker) 85. A Crooked Foot in Cross-section. (Gutenacker) 86. Sand-crack Firing-iron 87. Sand-crack Forceps and Clamp. (Vachette's) 88. McGill's Sand-crack Clamp 89. Koster's Sand-crack Clamp 90. Sand-crack Belt 91. Method of 'Easing' the Bearing of the Wall on the Shoe in the Treatment of Sand-crack 92. Method of 'Easing' the Bearing of the Wall on the Shoe in the Treatment of Sand-crack 93. Method of 'Easing' the Bearing of the Wall on the Shoe in the Treatment of Sand-crack 94 96. Grooving the Wall in the Treatment of Sand-crack 97. Removing the Wall in the Treatment of Sand-crack 98. Removing the Wall in the Treatment of Sand-crack 99. Horizontal Section of Corn. (Gutenacker) 100. Inner Surface of the Wall, showing Changes in Chronic Corn. (Gutenacker) 101. Perpendicular Section of the Wall in a Case of Chronic Corn. (Gutenacker) 102. Three-quarter Shoe 103. Three-quarter Bar Shoe 104. Shoe with a 'Dropped' Heel 105. Shoe with a 'Set' Heel 106. Curette, or Volkmann's Spoon 107. Resection of the Terminal Portion of the Perforans Tendon (Gutenacker) 108. Shoe with extended Toe-piece. (Colonel Nunn) 109. Mesian Section of Foot with Lesions following Coronitis. (Gutenacker) 110. Toe of Ordinary Hind-shoe 111. Toe of Hind-shoe Bevelled for the Prevention of Overreach 112. Hoof showing Lesion in the Wall following Coronitis. (Gutenacker) 113. Foot with Lesions of Chronic Coronitis. (Gutenacker) 114. Hoof Accidentally Tom from Foot. (Cartledge) 115. Hoof Accidentally Tom from Foot. (Rogerson) 116. Section of Foot with Laminitis of Eight Days' Duration. (Gutenacker) 117. Section of Foot with Laminitis of Fourteen Days' Duration. (Gutenacker) 118. Chronic Ostitis of the Os Pedis in Laminitis. 119. Broad's Rocker Bar Shoe for Laminitis. 120. The Foot showing Grooves made in the Wall for Treatment of Laminitis (Anterior Surface). 121. The Foot showing Grooves made for the Treatment of Laminitis (Solar Surface). 122. Foot with Chronic Laminitis. (Gutenacker) 123. Inferior Aspect of Foot with Chronic Laminitis. (Gutenacker) 124. Section of Foot with Laminitis of Three Weeks' Duration. (Gutenacker) 125. Section of Foot with Laminitis of Several Years' Duration. (Gutenacker) 126. Diagram showing Position of the Abnormal Growth of Horn in Chronic Laminitis. 127. Diagram showing the same Abnormal Growth of Horn Removed prior to Shoeing. 128. Shoe with Heel-clip. 129. Internal Seedy-Toe. 130. External Seedy-Toe. (Colonel Nunn) 131. External Seedy-Toe. (Colonel Nunn) 132. A Keraphyllocele on the Inner Surface of the Horn of the Wall at the Toe. (Gutenacker) 133. Os Pedis showing Absorption of Bone caused by the Pressure of a Keraphyllocele. (Gutenacker) 134. Foot with Canker of the Frog and Heels. (Gutenacker) 135. Foot with Canker extending to the Wall. (Malcolm) 136. Foot with Advanced Canker. (Gutenacker) 137. Feet affected with Specific Coronitis. (Taylor) 138. Fore-foot with Specific Coronitis. (Taylor) 139. Excision of the Lateral Cartilage (Old Method). (Gutenacker) 140. Excision of the Lateral Cartilage. (After Moller and Frick). (Gutenacker) 141. Excision of the Lateral Cartilage. (After Bayer.) (Gutenacker) 142. Partial Excision of the Lateral Cartilage 143. Ossified Lateral Cartilages, or Side-bones. 144. Smith's Side-bone Saw (Old Pattern). 145. Smith's Side-bone Saw (Improved Pattern). 146. Smith's Hoof Plane. 147. Hodder's Hoof Chisel. 148. Foot showing the Grooves made in Smith's Operation for Side-bones (viewed from the Side). 149. Foot showing the Grooves made in Smith's Operation for Side-bones (viewed from Below). 150. Periostitis involving the Pedal and Navicular Bones. (Litt) 151. Periostitis involving the Pedal and Navicular Bones. (Litt) 152. Effects of Periostitis on the Os Pedis. (Smith) 153. Effects of Periostitis on the Os Pedis. (Smith) 154. Effects of Periostitis on the Os Pedis. (Jones) 155. Effects of Periostitis on the Os Pedis. (Jones) 156. Case of Buttress Foot. (Routledge) 157. Foot showing Fracture of the Pyramidal Process in a Case of Buttress Foot. (Routledge) 158. Fracture of the Os Coronæ. (Crawford) 159. Fracture of the Os Coronæ. (Crawford) 160. Fractured Os Pedis. (Freeman) 161. Navicular Bone showing Lesions of Navicular Disease. (Gutenacker) 162. Foot with the Seat of Navicular Disease exposed (showing Lesions). (Gutenacker) 163. Navicular Bone showing Lesions of Navicular Disease (a Case of Long-standing). (Gutenacker) 164. Frog Seton Needle. 165. Diagram showing Course of the Needle in Setoning the Frog.
DISEASES OF THE HORSE'S FOOT
CHAPTER I
INTRODUCTION
The importance of that branch of veterinary surgery dealing with diseases of the horse's foot can hardly be overestimated. That the animal's usefulness is dependent upon his possession of four good feet is a fact that has long been recognised. Who, indeed, is there to be found entirely unacquainted with one or other of such well-known aphorisms as: 'Whoever hath charge of a horse's foot has the care of his whole body'; 'As well a horse with no head as a horse with no foot'; or the perhaps better known, and certainly more epigrammatic, 'No foot, no horse.'
Without taking these sayings literally, it will be admitted by almost everyone that they contain a vast amount of actual truth. This allowed, it at once becomes clear that a ready understanding of the diseases to which the foot is liable, the means of holding them in check, and the correct methods of treating them should figure largely in the knowledge at the command of the veterinary surgeon.
In the very great majority of instances the horse's ability to perform labour is the one thing that justifies his existence, and to that end the presence of four good, sound feet is an almost indispensable qualification. And yet how many circumstances do we see tending to militate against that one essential.
Even in colthood the foot, if neglected, may become a source of trouble. Unless periodically examined and properly trimmed, its shape is liable to serious alteration. From that in which it is best calculated to withstand the effects of the wear it will be called upon to endure in after life, it may become so changed for the worse as to seriously affect the animal's value.
In the matter of feeding, too, trouble is likely to ensue. Particularly is this the case where the colt shows points of exceptional merit. He is 'got up' for show, and the feet are likely to fall victims to the mismanagement that frequent exhibition so often carries with it. An extra allowance of peas, beans, wheat, or other equally injurious food is given. The result is a severe attack of laminitis, and an otherwise valuable and promising colt is permanently ruined.
Exposed as it is, too, to injury, the foot of a young horse, even at grass, is frequently the seat of injuries from picked up nails, stakes, or other agents which, unless detected and carefully treated, may terminate in a troublesome case of quittor and incurable lameness.
With the passing of colthood, and the coming into effect of the evils of further domestication, the troubles to which the foot is open become more numerous. Foremost among them will come those having their starting-point in errors of practice originating in the forge; for, in spite of attempts at their education, smiths, as a class, are as yet grievously unversed in even the elementary knowledge of the delicate construction of the member that is entrusted to their care.
This fact has been dilated on in books devoted to shoeing, and in the prefatory note to the last edition of Fleming's manual on this subject we find the following statement: 'The records of all humane societies show that, of prosecutions for cruelty to animals, an overwhelming majority refer to the horse; and of these, a large proportion are for working horses while suffering from lameness in one form or other.
'So frequent are such cases that observers have concluded that their prevalence must result from some specific cause, and, not unnaturally, attention has thus been directed to the various modes of management practised in relation to the horse's foot, to the manner of shoeing, and, in particular, to the way in which the foot is prepared for the shoe.'
It must be remembered, however, that although harm in the forge may frequently arise from culpable roughness or carelessness, such is not necessarily always the case, and that quite as much injury may result from careful and conscientious workmanship when it is unfortunate enough to be based upon principles wrong in themselves to commence with.
It so happens, too, that shoeing, in itself a necessary evil, may be responsible for injuries in the causation of which the smith can have played no part. Take, for example, the ill effects following upon the animal's attendant allowing him to carry his shoes for too long a time. In this case the natural growth of the horn carries the heel of the shoe further beneath the foot than is safe for a correct bearing; in fact, anterior to the point of inflection of the wall. The shoe, at the same time, is greatly thinned from excessive wear. Result, a sharp and easily-bended piece of iron situate immediately under the seat of corn. Pressure or actual cutting of the sole is bound to occur, and the animal is lamed.
Again, apart from the question of negligence or otherwise on the part of the smith or the animal's attendant, it must be remembered that the nailing on to the foot of a plate of iron is not giving to the animal an easier means of progression. The reverse is the case. In place of the sucker-like face of the natural horn is substituted a smooth, and, with wear, highly-polished surface. Slipping and sliding attempts to gain a foothold become frequent, and strains of the tendons and ligaments follow in their wake.
As, however, this treatise is not intended to deal with the art of shoeing, the reader must be referred to other works for further information. In addition to Fleming's, there may be mentioned, among others, Hunting's 'Art of Horse Shoeing,' and the very excellent volume of Messrs. Dollar and Wheatley on the same subject. Leaving the forge, we may next look to the nature of the animal's work, and the conditions under which he is kept, for active causes in the production of disorders of the foot. From the yielding softness of the pasture he is called to spend the bulk of his time upon the hard macadamized tracks of our country roads, or the still more hard and more dangerous asphalt pavings or granite sets of our towns. The former, with the bruises they will give the sole and frog from loose and scattered stones, and the latter, with the increased concussion they will entail on the limb, are active factors in the troubles with which we are about to deal. Upon these unyielding surfaces the horse is called to carry slowly or rapidly, as the case may be, not only his own weight, but, in addition, is asked to labour at the hauling of heavy loads. The effects of concussion and heavy traction combined are bound primarily to find the feet, and such diseases as side-bones, ringbones, corns, and sand-cracks commence to make their appearance.
Again, as opposed to the comparative healthiness of the surroundings when at grass, consideration must be given to the chemical changes the foot is frequently subjected to when the animal is housed.
Only too often the bedding the animal has to stand upon for several hours of the twenty-four can only be fitly described as 'filthy in the extreme.' The ammoniacal exhalations from these collected body-discharges must, and do, have a prejudicial effect upon the nature of the horn, and, though slow in its progress, mischief is bound sooner or later to occur in the shape of a weakened and discharging frog, with its concomitant of contracted heels. Lucky it is in such a case if canker does not follow on.
Observers, too, have chronicled the occurrence in horse's feet of disease resulting from the use of moss litter. Tenderness in the foot is first noticeable, which tenderness is afterwards followed by a peculiar softening of the horn of the sole and the frog. What should be a dense, fairly resilient substance is transformed into a material affording a yielding sensation to the fingers not unlike that imparted by a soft indiarubber, and as easily sliced as cheese-rind.
Lastly, though the foot is extremely liable to suffer from the effects of extreme dryness or excessive humidity, especially with regard to the changes thus brought about in the nature of the horn, it is perforce exposed at all times to the varying condition of the roads upon which it must travel. The intense dryness of summer and the constant damp of winter, each in their turn take part in the deteriorating influences at work upon it.
Though this subject might be indefinitely prolonged, this brief résumé of the adverse circumstances to which the foot of the horse is exposed is sufficient to point out the extreme importance of its study to the veterinary surgeon. So long as the horse is used as a beast of burden so long will this branch of veterinary surgery offer a wide and remunerative field of labour.
CHAPTER II
REGIONAL ANATOMY
Considered from a zoological standpoint, the foot of the horse will include all those parts from the knee and hock downwards. For the purposes of this treatise, however, the word foot will be used in its more popular sense, and will refer solely to those portions of the digit contained within the hoof. When, in this chapter on regional anatomy, or elsewhere, the descriptive matter or the illustrations exceed that limit, it will be with the object of observing the relationship between the parts we are concerned with and adjoining structures.
Taking the limit we have set, and enumerating the parts within the hoof from within outwards, we find them as follows:
A. THE BONES.--The lower portion of the second phalanx or os coronæ; the third phalanx, os pedis, or coffin bone; and the navicular or shuttle bone.
B. THE LIGAMENTS.--The ligaments binding the articulation.
C. THE TENDONS.--The terminal portions of the extensor pedis and the flexor perforans.
D. THE ARTERIES.
E. THE VEINS.
F. THE NERVES.
G. THE COMPLEMENTARY APPARATUS OF THE OS PEDIS.
H. THE KERATOGENOUS MEMBRANE.
I. THE HOOF.
A. THE BONES.
THE SECOND PHALANX, OS CORONÆ, OR SMALL PASTERN BONE.--This belongs to the class of small bones, in that it possesses no medullary canal. It is situated obliquely in the digit, running from above downwards and from behind to before, and articulating superiorly with the first phalanx or os suffraginis, and inferiorly with the third phalanx and the navicular bone.
FIG. 1.--THE BONES OF THE PHALANX. 1, The os suffraginis; 2, the os coronæ; 3, the os pedis; 4, the navicular bone, hidden by the wing of the os pedis, is in articulation in the position indicated by the barbed line.
FIG. 2.--SECOND PHALANX OR OS CORONÆ (ANTERIOR VIEW). 1, Anterior surface; 2, superior articulatory surface; 3, inferior articulatory surface; 4, pits for ligamentous attachment.
FIG. 3.--SECOND PHALANX OR OS CORONÆ (POSTERIOR VIEW). 1, Posterior surface; 2, gliding surface for passage of flexor perforans; 3, lower articulatory surface.
Cubical in shape, it is flattened from before to behind, and may be described as possessing six surfaces: An anterior surface, covered with slight imprints; a posterior surface, provided above with a transversely elongated gliding surface for the passage of the flexor perforans; two lateral surfaces, each rough and perforated by foraminæ, and each bearing on its lower portion a thumb-like imprint for ligamentous attachment, and for the insertion of the bifid extremity of the perforatus tendon; a superior surface, bearing two shallow articular cavities, separated by an antero-posterior ridge, for the accommodation of the lower articulating surface of the first phalanx; an inferior surface, also articulatory, which in shape is obverse to the superior, bearing two unequal condyles, separated by an ill-defined antero-posterior groove, which surface articulates with the os pedis and the navicular bone.
Development.--The bone usually ossifies from one centre, but often there is a complementary nucleus for the upper surface.
THE THIRD PHALANX, OS PEDIS, OR COFFIN BONE.--This also belongs to the class of short bones. It forms the termination of the digit, and, with the navicular bone, is included entirely within the hoof. For our examination it offers three surfaces, two lateral angles, and three edges.
The Anterior or Laminal Surface, following closely in contour the wall of the hoof, is markedly convex from side to side, nearly straight from above to below, and closely dotted with foraminæ of varying sizes. On each side of this surface is to be seen a distinct groove, the preplantar groove, or preplantar fissure, which, commencing behind, between the basilar and retrossal processes, runs horizontally forwards from the angles or wings of the bone, and terminates anteriorly in one of the larger foraminæ. As the name 'laminal' indicates, it is this surface which in the fresh state is covered by the sensitive laminæ.
The Inferior or Plantar Surface, hollowed in the form of a low arch, presents for our inspection two regions, an anterior and a posterior, divided by a well-marked line, the Semilunar Crest, which extends forward in the shape of a semicircle. The anterior region, as is the laminal surface, is covered with foraminæ; in this case more minute. In the recent state it is covered by the sensitive sole. The posterior region, lying immediately behind the semilunar crest, shows on each side of a median process a large foramen, the Plantar Foramen. From this foramen runs the Plantar Groove, a channel, bounded above by the superior edge, and below by the semilunar crest of the bone, which conducts the plantar arteries into the Semilunar Sinus, a well-marked cavity in the interior of the bone.
The Superior or Articular Surface consists of two shallow depressions, divided by a slight median ridge. Its posterior part shows a transversely elongated facet for articulation with the navicular bone.
The Superior Edge, outlining the superior margin of the laminal surface, describes a curve, with the convexity of the curve forward. In the centre of the curve is a triangular process, the Pyramidal Process, which serves as the point of attachment of the extensor pedis.
The Inferior Edge, the most extensive of the three, separates the laminal from the solar surface. It is semicircular in shape, sharp, and finely dentated, and is perforated by eight to ten large foraminæ.
The Posterior Edge, very slightly concave, divides the small, transversely elongated facet of the superior surface from the posterior region of the inferior surface.
The Lateral Angles of the bone, also termed the Wings, are two projections directed backwards. Each is divided by a cleft into an upper, the Basilar Process, and a lower, the Retrossal Process. In old animals the posterior portion of the cleft separating the two processes gradually becomes filled in with bony deposit, thus transforming the cleft into a foramen, which gives passage to the preplantar artery. We may mention in passing that the lateral angles give attachment to the lateral fibro-cartilages, and that the lateral angles themselves in old horses become increased in size owing to ossification of portions of the adjacent lateral cartilages.
Development.--The os pedis ossifies from two centres, one of which is for the articular surface; but this epiphysis fuses with the rest of the bone before birth.
FIG. 4.--THIRD PHALANX OR OS PEDIS (POSTERO-LATERAL VIEW). 1, Anterior or laminal surface; 2, preplantar foramen; 3, preplantar groove; 4, basilar process of the wing; 5, retrossal process of the wing; 6, foramen caused by the ossifying together posteriorly of the basilar and retrossal processes.
FIG. 5.--THIRD PHALANX OR OS PEDIS (VIEWED FROM BELOW). 1, Plantar surface; 2, plantar foramen and plantar groove; 3, semilunar crest; 4, tendinous surface; 5, retrossal processes of the wings.
THE NAVICULAR BONE, SHUTTLE BONE, OR SMALL SESAMOID.--Placed behind the articulating point of the second and third phalanges, this small shuttle-shaped bone assists in the formation of the pedal articulation. It is elongated transversely, flattened from above to below, and narrow at its extremities. In it we see two surfaces, and two borders.
The Superior or Articular Surface of the bone, which may easily be recognised by its smoothness, is moulded upon the lower articular surface of the second phalanx, being convex in its middle, and concave on either side.
The Inferior or Tendinous Surface resembles the preceding in form, but is broader and less smooth. In the recent state it is covered with fibro-cartilage for the passage of the flexor perforans.
The Anterior Border possesses above a small transversely elongated facet for articulation with the os pedis, and below a more extensive grooved portion, perforated by numerous foraminæ, affording attachment to the interosseous ligaments of the articulation.
The Posterior Border, thick in the middle, but thinner towards the extremities, is roughened for ligamentous attachment.
Development.--The bone ossifies from a single centre.
B. THE LIGAMENTS.
THE ARTICULATION OF THE FIRST WITH THE SECOND PHALANX, OR THE PASTERN JOINT.--Adhering to the limit we have set, this articulation should not receive our attention. As, however, we shall in a later page be concerned with fractures of the os coronæ, which fractures may affect the articulation above mentioned, a brief note of its formation will not be out of place.
It is an imperfect hinge-joint, permitting of extension and flexion, allowing the first phalanx to pivot on the second, and admitting of the performance of slight lateral movements. It is formed by the opposing of the inferior surface of the os suffraginis with the superior surface of the os coronæ. The articulating surface of the os coronæ is supplemented by the addition behind of a thick piece of fibro-cartilage (the glenoid) attached inferiorly to the posterior edge of the upper articulatory surface of the os coronæ, and superiorly by means of three fibrous slips on each side to the os suffraginis. The innermost of these three slips becomes attached to about the middle of the lateral edge of the suffraginis, and the remaining two, beneath the first, attach themselves to nearer the lower end of that bone. The posterior surface of the complementary cartilage forms a gliding surface for the passage of the perforans.
FIG. 6.--THE NAVICULAR BONE (VIEWED FROM BELOW). 1, Inferior surface (smooth for the passage of the flexor perforans); 2, anterior edge of inferior surface; 3, posterior edge of inferior surface.
FIG. 7.--THE NAVICULAR BONE (VIEWED FROM ABOVE, THE BONE TILTED POSTERIORLY TO SHOW ITS ANTERIOR BORDER). 1, Superior articulatory surface; 2, anterior border (grooved portion of); 3, anterior border (articulatory portion of).
[Illustration: FIG. 8.--LIGAMENTS OF THE FIRST AND SECOND INTERPHALANGEAL ARTICULATIONS (VIEWED FROM THE SIDE). (AFTER DOLLAR AND WHEATLEY.) 1, Outermost slip from the glenoidal fibro-cartilage; 2, lateral ligament of the first interphalangeal articulation; 3, prolongations of the lateral ligament of the first interphalangeal articulation attached to the end of the navicular bone to form the postero-lateral ligament of the pedal joint; 4, end of the navicular bone; 5, antero-lateral ligament of the pedal joint.]
The Lateral Ligaments.--These are large and thick, an outer and an inner, running obliquely from above downwards and backwards. Each is inserted superiorly into the lateral tubercle of the lower end of the first phalanx, and inferiorly to the side of the second phalanx, their most inferior fibres becoming finally fixed to the extremities of the navicular bone, where they form the postero-lateral ligaments of the pedal articulation. In front of the joint the extensor pedis plays the part of an additional ligament.
The Synovial Membrane.--This is limited in front by the tendon of the extensor pedis, on each side by the lateral ligaments of the joint, and behind by the glenoid fibro-cartilage. At this point it is prolonged upwards as a pouch behind the lower extremity of the first phalanx.
THE ARTICULATION OF THE SECOND PHALANX WITH THE THIRD, THE PEDAL, OR THE COFFIN JOINT.--This also is an imperfect hinge-joint, permitting only of flexion and extension, which movements are more restricted than in the previous articulation. Three bones enter into its formation: the second phalanx, the third phalanx, and the navicular bone. The lower articulatory surface is formed by the third phalanx and the navicular bone combined. To effect this the navicular is closely and firmly attached to the third phalanx by an interosseous ligament. The two bones, as one, are then connected to the second phalanx by four lateral ligaments, an anterior and a posterior on each side.
The Interosseous Ligament consists of extremely short fibres running from the extensively grooved portion of the anterior surface of the navicular bone to become attached to the os pedis immediately behind its articular surface.
The Antero-lateral Ligaments are attached by their superior extremities to the lateral surfaces of the second phalanx, and by their inferior extremities into the depressions on either side of the pyramidal process of the os pedis.
The Postero-lateral Ligaments.--As mentioned when describing the first interphalangeal articulation, these are in reality continuations of the lateral ligaments of that joint. Running obliquely downwards and backwards from their point of attachment to the first phalanx they curve round the lower part of the side of the second phalanx and end on the extremities and posterior surface of the navicular bone. Having reached that position, they send short attachments to the retrossal process of the os pedis and to the inner face of the lateral cartilage.
[Illustration: FIG. 9.--LIGAMENTS OF THE FIRST AND SECOND INTERPHALANGEAL ARTICULATIONS (VIEWED FROM BEHIND). (AFTER DOLLAR AND WHEATLEY.) 1, Suspensory ligament; 2, innermost slip from complementary cartilage of pastern joint; 3, middle slip from complementary cartilage of pastern joint; 4, outermost slip from complementary cartilage of pastern joint; 5, glenoid or complementary cartilage of pastern joint; 6, postero-lateral ligaments of the pedal joint; 7, the navicular bone; 8, interosseous ligaments of the pedal joint; 9, semilunar crest of os pedis; 10, plantar surface of os pedis.]
Synovial Membrane.--This extends below the facets uniting the navicular to the pedal bone, and offers for consideration two sacs. A large one posteriorly running up behind the second phalanx to nearly adjoin the sesamoidean bursæ, and a small one, a prolongation of the synovial membrane between the antero-lateral and postero-lateral ligaments of the same side. This latter is often distended, and on account of its close proximity to the seat of operation, is liable to be accidentally opened in excision of the lateral cartilage for quittor.
C. THE TENDONS
In order to convey an intelligent understanding of the tendons it will be wise to briefly describe the course of their parent muscles from their commencement.
THE EXTENSOR PEDIS.--The extensor pedis arises from the lower extremity of the humerus in two distinct portions of unequal size, a muscular and a tendinous. These are succeeded by two tendons passing in common through a vertical groove at the lower end of the radius. Lower in the limb these tendons separate, the outer and smaller joining the tendon of the extensor suffraginis, and the inner and main tendon continuing its course downwards. With the exception of the navicular, it is attached to all the bones of the foot, and is covered internally by the capsular ligaments of the joints over which it passes, those with which we are concerned being the pastern joint and the pedal joint. Before its attachment to the os pedis it receives on each side of the middle of the first phalanx reinforcement in the shape of a strong band descending obliquely over the fetlock from the suspensory ligament. Widening out in fanlike fashion, it is inserted into the pyramidal process of the os pedis.
Action.--The action of this muscle is to extend the third phalanx on the second, the second on the first, and the first on the metacarpus. It also assists in the extension of the foot on the forearm.
[Illustration: FIG. 10.--THE FLEXOR TENDONS AND EXTENSOR PEDIS. (AFTER HAÜBNER.) 1, Tendon of flexor perforans; 2, its supporting check-band from the posterior ligament of the carpus; 3, tendon of the flexor perforatus; 4, ring and sheath of the flexor perforatus; 5, widening out of the flexor perforatus to form the plantar aponeurosis; 6, suspensory ligament; 7, reinforcing band from the suspensory ligament to the extensor pedis; 8, the extensor pedis.]
THE FLEXOR PEDIS PERFORATUS, OR THE SUPERFICIAL FLEXOR OF THE PHALANGES.--In common with the perforans, this muscle arises from the inner condyloid ridge of the humerus. It is reinforced at the lower end of the radius by the superior carpal ligament, passes through the carpal and metacarpo-phalangeal sheaths, and, arriving behind the fetlock, forms a ring for the passage of the flexor perforans. Its termination is bifid, and it is inserted on either side to the lateral surface of the second phalanx.
[Illustration: FIG. 11.--THE FLEXOR PERFORANS AND FLEXOR PERFORATUS TENDONS. The metacarpo-phalangeal sheath and the ring of the perforatus laid open posteriorly, and the cut edges reflected to show the passage of the perforans. 1, Reflected cut edges of the perforatus ring and the metacarpo-phalangeal sheath; 2, the perforans tendon; 3, point of insertion of the perforans tendon into the semilunar crest of the os pedis (this widened and thickened extremity of the perforans is known as the plantar aponeurosis).]
[Illustration: FIG. 12.--THE FLEXOR PERFORATUS AND FLEXOR PERFORANS TENDONS. The metacarpo-phalangeal sheath and the ring of the perforatus laid open posteriorly, and the cut edges reflected; the flexor perforans cut through at about the region of the sesamoids, and its inferior portion deflected. 1, Superior end of severed perforans tendon; 2, inferior end of severed perforans tendon; 3, insertion of flexor perforans into semilunar crest of os pedis; 4, the cut and reflected edges of the metacarpo-phalangeal sheath and perforatus ring; 5, the bifid insertion of the flexor perforatus into the lateral surfaces of the os corona; 6, the capsular ligament of the pedal joint; 7, the navicular bone; 8, the posterior surface and glenoid fibro-cartilage of the os coronæ.]
Action.--This muscle flexes the second phalanx on the first, the first on the metacarpus, and the entire foot on the forearm. Mechanically, it acts as a stay when the animal is standing by maintaining the metacarpo-phalangeal angle.
[Illustration: FIG. 13.--MEDIAN SECTION OF FOOT. A, Os suffraginis; B, os coronæ; C, os pedis; D, navicular bone; E, tendon of the extensor pedis; F, insertion of the extensor pedis into the pyramidal process of the os pedis; G, the tendon of the flexor perforatus; H, insertion of perforatus into the os coronæ; I, tendon of the flexor perforans; J, its passing attachment to the os coronæ; K, its final insertion into the semilunar crest of os pedis; a, section of coronary cushion; b, section of plantar cushion; c, semilunar sinus of os pedis.]
THE FLEXOR PEDIS PERFORANS, OR THE DEEP FLEXOR OF THE PHALANGES.--This muscle consists of three easily-divided portions: an ulnar, a humeral, and a radial, and has for points of origin the olecranon process of the ulna, the inner condyloid ridge of the humerus, and the posterior surface of the radius. These portions are continued by a common tendon which enters the carpal sheath with the tendon of the perforatus, and continues with it through the synovial sheath of the metacarpo-phalangeal region. Like the last-named tendon, it receives a supporting check-band, in this case from the posterior ligament of the carpus. Passing down between the suspensory ligament in front, and the perforatus tendon behind, it glides over the sesamoid pulley and passes through the ring formed by the perforatus. Continuing its course, it passes between the bifurcating portions of the extremity of the perforatus, glides over the smooth posterior surface of the supplementary glenoid cartilage of the articulation of the first and second phalanges, plays over the inferior surface of the navicular bone, and finally becomes inserted into the semilunar crest of the os pedis. On reaching the posterior border of the navicular bone it widens out to form the plantar aponeurosis.
In connection with the lower portion of this tendon must be noticed the Navicular Sheath. This is a synovial sheath lining the deep face of the tendon, and reflected on to the navicular bone and the interosseous ligament of the pedal joint. This will be of particular interest when we come to deal with cases of pricked foot from picked up nails. Above, it is in connection with the synovial membrane of the pedal articulation and that of the metacarpo-phalangeal sheath.
Action.--The action of the perforans is to flex the third on the second, and the second on the first phalanx. The latter it flexes in turn on the metacarpus. It also assists in the flexion of the entire foot on the forearm, and in supporting the angle of the metacarpo-phalangeal articulation when the animal is standing.
D. THE ARTERIES.
So far as the arteries supplying the foot are concerned, we shall be interested in following up the distribution of the two digitals, which are the terminal branches of the Large Metacarpal.
THE LARGE METACARPAL, OR COLLATERAL ARTERY OF THE CANNON.--This, the larger terminal branch of the posterior radial artery, needs brief mention, for the reason that we shall be afterwards concerned with it in the operation of neurectomy. Its point of origin is the inside of the inferior extremity of the radius. Descending in company with the flexor tendons, and passing behind the carpus and beneath the carpal sheath, it continues its descent, in company with the internal plantar nerve and the internal metacarpal vein, on the inner side of the flexor tendons until just above the fetlock. At this point it bifurcates into the digital arteries.
From the carpus downwards the large metacarpal artery, the internal metacarpal vein, and the internal plantar nerve are in close relation with each other. The vein holds the anterior position. The artery is between the two, and has the nerve in close contact with it behind.
THE DIGITAL ARTERIES, OR COLLATERAL ARTERIES OF THE DIGIT.--These are of large volume, and carry the blood to the keratogenous apparatus of the foot. They separate from each other at an acute angle, and pass over the side of the fetlock, one to the inside, the other to the outside, to reach the internal face of the basilar process of the os pedis, where they bifurcate to form the Plantar and Preplantar arteries. In the whole of their course the digital arteries follow the flexor tendons, and are related in front to the digital vein, and behind to the posterior branch of the plantar nerve. This is the nerve implicated in the lower operation of neurectomy, and its relation to adjoining structures will be detailed under Section F. of this chapter. During its course the digital artery gives off branches in the following positions:
1. At the Fetlock numerous branches to the metacarpo-phalangeal articulation, the sesamoid sheath, and the tendons.
2. At the Upper Extremity of the First Phalanx branches for the supply of the surrounding tissues, and for the tissues of the ergot.
3. Towards the Middle of the Third Phalanx, the Perpendicular artery of Percival. This arises at a right angle from the main vessel, and immediately divides into two series of ramifications--an ascending and a descending. The ramifications of these series freely anastomose with corresponding vessels of the opposite side.
4. At the Superior Border of the Lateral Cartilage, the Artery of the Plantar Cushion. This is directed obliquely downwards and backwards, under cover of the cartilage, and is distributed to the middle portion of the complementary apparatus of the os pedis, as well as to the villous tissue and the coronet. A branch of it is turned forwards to join with the coronary circle in forming the circumflex artery of the coronet.
[Illustration: FIG. 14.--THE ARTERIES OF THE FOOT. The digital; 2, the perpendicular--(a) its ascending branch, (b) its descending branch; 3, circumflex artery of coronary cushion; 4, the preplantar (ungual) artery--this is seen issuing from the preplantar foramen, and distributing numerous ascending (c) and descending (d) branches (the latter concur in forming the circumflex artery of the toe); 5, the circumflex artery of the toe; 6, at the point marked (*) the terminal branch of the digital--namely, the plantar ungual--is hidden behind the lateral cartilage; 7, the lateral cartilage.]
5. Under the Lateral Cartilage two transverse branches, an anterior and a posterior, to form the Coronary Circle. The numerous ramifications of these branches anastomose both anteriorly and posteriorly with their corresponding branches of the artery of the opposite side. This circle closely embraces the os coronæ. Among the larger branches given off from its anterior portion are two descending, one on each side of the extensor pedis, to assist in the formation of the Circumflex Artery of the Coronary Cushion. The formation of this last-named artery is completed posteriorly by the before-mentioned branch from the artery of the plantar cushion.
THE PREPLANTAR (UNGUAL[A]) ARTERY.--This, the smaller of the two terminal branches of the digital, is situated inside the basilar process of the os pedis. It turns round this to gain the fissure between the basilar and retrossal processes, and becomes lodged in the preplantar fissure. Here it terminates in several divisions which bury themselves in the os pedis. Before leaving the inner aspect of the pedal wing it supplies a deep branch to the heel and the villous tissue. Gaining the outer aspect of the wing, it distributes a further backward branch, which passes behind the circumflex artery of the pedal bone, and, during its passage in the preplantar fissure, gives off ascending and descending branches, which ramify in the laminal tissue.
THE PLANTAR (UNGUAL[A]) ARTERY.--This, the larger of the two terminals of the digital, may be looked upon as a continuation of the main vessel. Running along the plantar groove, it gains the plantar foramen. Here it enters the interior of the bone (the semilunar sinus) and anastomoses with the corresponding artery of the opposite side. The circle of vessels so formed is called the Plantar Arch or the Semilunar Anastomosis.
[Footnote A: The epithet 'ungual' is added by Chauveau to distinguish these arteries from the properly so-called plantar arteries--the terminal divisions of the posterior tibial artery.]
From the semilunar anastomosis radiate two main groups of arterial branches, an ascending group and a descending one. The ascending branches penetrate the substance of the os pedis, and emerge by the numerous foraminæ on its laminal surface. The descending branches, larger in size, also penetrate the substance of the pedal bone, and emerge in turn from the foraminæ cribbling its outer surface--in this case the set of larger foraminæ opening on its inferior edge. Having gained exit from the bone, their frequent anastomosis, right and left, with their fellows forms a large vessel following the contour of the inferior edge of the os pedis. This constitutes the Circumflex Artery of the Toe.
E. THE VEINS.
These commence at the foot with a series of plexuses, which may be described as forming (1) AN INTERNAL OR INTRA-OSSEOUS VENOUS SYSTEM, and (2) AN EXTERNAL OR EXTRA-OSSEOUS VENOUS SYSTEM.
1. THE INTRA-OSSEOUS VENOUS SYSTEM.--This is a venous system within the structure of, and occupying the semilunar sinus of the os pedis. It follows in every respect the arrangement of the arteries as before described in the same region. Efferent vessels emerge from the plantar foraminæ, follow the plantar fissures, and ascend within the basilar processes of the os pedis. Here they lie under shelter of the lateral cartilages, and assist in the formation of the deep layer of the coronary plexus of the extra-osseous system.
2. THE EXTRA-OSSEOUS VENOUS SYSTEM.--This may be regarded as a close-meshed network enveloping the whole of the foot. Although a continuous system, it is best described by recognising in it three distinct parts:
(a) The Solar Plexus.
(b) The Podophyllous Plexus.
(c) The Coronary Plexus.
(a) The Solar Plexus.--The veins of this plexus discharge themselves in two directions: (1) By a central canal or canals running along the bottom of the lateral lacunæ of the plantar cushion to gain the deep layer of the coronary plexus. (2) By the Circumflex or Peripheral Vein of the Toe, a canal formed by ramifications from the solar and the podophyllous plexuses, and following the direction of the artery of the same name. The circumflex vein terminates by forwarding branches to concur in the formation of the superficial coronary plexus.
(b) The Podophyllous or Laminal Plexus.--The podophyllous veins anastomose below with the circumflex vein of the solar plexus, and above with the veins of the coronary plexus.
(c) The Coronary Plexus.--This proceeds from the podophyllous, the intra-osseous, and the solar networks, and consists of a central and two lateral parts.
The central portion lies between the lateral cartilages and immediately under the coronary cushion. The lateral portions are ramifications on both surfaces of the lateral cartilages. The ramifications on the lateral cartilages may be again distinguished as superficial and deep. The superficial layer is distributed over the external face of the cartilage, forming thereon a dense network, and finally converges towards the superior limit of the plexus to form ten or twelve principal branches, which again unite to form two large vessels. These vessels, by their final fusion at the lower end of the first phalanx, constitute the digital vein. The deep layer is formed, as before described, by ascending branches from the posterior parts of the podophyllous and solar plexuses, and by branches from the intra-osseous system of the pedal bone. The veins of this deep layer finally drain into the two vessels proceeding from the superficial layer, which go to the formation of the digital vein.
THE DIGITAL VEINS--These arise from the network formed on the surfaces of the lateral cartilages, and ascend in front of the digital arteries to unite above the fetlock, where they form an arch between the deep flexor and the suspensory ligament. From this arch (named the Sesamoidean) proceed the Metacarpal Veins.
THE METACARPAL VEINS.--Three in number, they are distinguished as an Internal and an External Metacarpal, and a Deep or Interosseous Metacarpal. As we shall be concerned with these in the higher operation of neurectomy, we may give them brief mention.
THE INTERNAL METACARPAL VEIN, the largest of the three, has relations with the internal metacarpal artery and the internal plantar nerve. These relations were shortly discussed under the section devoted to the arteries, to which the reader may refer.
THE EXTERNAL METACARPAL VEIN.--This ascends on the external side of the flexor tendons in company with the external plantar nerve.
The Interosseous Vein.--This is an irregular vessel running up between the suspensory ligament and the posterior face of the large metacarpal bone.
F. THE NERVES.
THE PLANTAR NERVES.--These are two in number, and are distinguished as Internal and External.
THE INTERNAL PLANTAR NERVE lies behind and in close contact with the great metacarpal artery during that vessel's course down the region of the cannon. A point of interest is that it gives off at about the middle of the cannon a branch which bends obliquely downwards and behind the flexor tendons to join its fellow of the opposite side--namely, the external plantar. This it joins an inch or more above the bottom of the splint bone. Measured in a straight line, this is about 2-1/2 inches below its point of origin. Near the fetlock, at the level of the sesamoids, the internal plantar nerve ends in several digital branches.
THE EXTERNAL PLANTAR NERVE.--This holds a position to the outside of the metacarpal region, analogous to that of the internal plantar nerve on the inside of the limb, running down on the external edge of the flexor tendons. Unlike the internal nerve, it is accompanied by a single vessel only, the external metacarpal vein, behind which it lies. At the level of the sesamoid bones it divides, as does the internal nerve, into three main branches--the digital nerves.
[Illustration: FIG. 15.--THE VEINS AND NERVES OF THE FOOT. 1, The digital vein; 2, its main tributaries, draining the podophyllous plexus, and concurring to form the digital; 3. the digital artery (the main trunk only of this is shown, in order to show its relationship with the vein and nerve); 4, the plantar nerve, with its three branches--(a) the anterior digital, (b) the middle digital, (c) the posterior digital; 5, the podophyllous plexus; 6, superficial portion of the coronary plexus; 7, the peripheral or circumflex vein of the toe.]
THE DIGITAL NERVES.--These are distinguished as Anterior, Middle, and Posterior.
The Anterior Branch descends in front of the vein, distributing cutaneous branches to the front of the digit, and terminating in the coronary cushion.
The Middle Branch descends between the artery and the vein, and freely anastomoses with the two other branches. It terminates in the coronary cushion and the sensitive laminæ.
The Posterior Branch.--This is the largest of the three, and may be regarded as the direct continuation of the plantar. At the fetlock it is placed immediately above the digital artery, but afterwards takes up a position directly behind that vessel. Together with the digital artery it descends to near the basilar process of the os pedis. Here it passes with the plantar artery into the interior of the os pedis, and continues its main branch, with the preplantar artery, in the fissure of the same name, to finally furnish supply to the os pedis and the sensitive laminæ. It is this nerve which is divided in the low operation of neurectomy.
Beyond the fact of this branch descending, in the region of the pastern, 1 inch behind the digital artery, a further point of interest presents itself to the surgeon, and one to which attention must be paid. This is the presence in close proximity to the nerve of the Ligament of the Pad (Percival), or the Ligament of the Ergot (McFadyean). This is a subcutaneous glistening cord originating in the ergot of the fetlock, passing in an oblique direction downwards and forwards, and crossing over on its way both the digital artery and the posterior branch of the digital nerve.
In the foregoing description of the anatomy, we have taken the fore-limb as our guide. In the hind-limb, where they reach the foot, the counterparts of the tendons, arteries, veins, and nerves differ in no great essential from their fellows in the fore. They will therefore need no special mention.
G. THE COMPLEMENTARY APPARATUS OF THE OS PEDIS.
This consists of two lateral pieces, the LATERAL CARTILAGES or Fibro-cartilages of the pedal bone, united behind and below by the Plantar Cushion.
1. THE LATERAL CARTILAGES.--Each is a flattened plate of cartilage, possessing two faces and four borders separated by four angles.