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Diseases of the Horse's Foot

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Title: Diseases of the Horse's Foot

Author: Harry Caulton Reeks

Release Date: February 21, 2004 [EBook #11204]

Language: English

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Produced by Juliet Sutherland, Leonard D Johnson and the Online Distributed Proofreading Team.

PREFACE

DISEASES

THE HORSE'S FOOT

H. CAULTON REEKS

Fellow of the Royal College of Veterinary Surgeons Author of 'The Common Colics of the Horse'

1906

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.

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.

INTRODUCTION

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

CONTENTS CHAPTER I

CHAPTER II

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

METHOD OF EXAMINING THE FOOT

GENERAL REMARKS ON OPERATIONS ON THE FOOT

CHAPTER IV

CHAPTER V

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

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

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

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

CHAPTER VI

CHAPTER VII

CHAPTER VIII

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

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

CHAPTER X

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 Phalanx2. 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 Perforatus12. The Flexor Perforans and Perforatus (the Perforans cut through and deflected)13. Median Section of Normal Foot14. The Arteries of the Foot15. The Veins and Nerves of the Foot16. The Lateral Cartilage17. The Keratogenous Membrane (viewed from the Side)18. The Keratogenous Membrane (viewed from Below)19. The Wall of the Hoof20. Internal Features of the Hoof21. Inferior Aspect of the Hoof22. Hoof with the Sensitive Structures removed23. Section of Epidermis24. Section of Skin with Hair Follicle and Hair25. Section of Human Nail and Nail-bed26. 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 Wall33. Horizontal Section through the Junction of the Wall with the Sole34. Section of Frog. (Mettam)35. Professor Lungwitz's Apparatus for Examining the Foot Movements36. Professor Lungwitz's Apparatus for Examining the Foot Movements37. The Movements of the Solar and Coronary Edges of the Hoof illustrated.(Lungwitz) 38. The Blind39. The Side-line40. Method of securing the Hind-foot with the Side-line41. The Hind-foot secured with the Side-line42. The Casting Hobbles43. Method of securing the Hind-leg upon the Fore44. The Hind-leg secured upon the Fore45. The Drawing-knife (Ordinary Pattern)46. Modern Forms of Drawing-knives47. Symes's Knife48-51. Illustrating Colonel Nunn's Method of applying a Poultice to the Foot52. Poultice-boot of Canvas and Steel53. Poultice-boot of Cocoa-fibre54. Foot-swab55. The Shoe with Plates

56. Quittor Syringe57. The Esmarch Bandage and Tourniquet58. Tourniquet with Wooden Block59. Neurectomy Bistoury60. Neurectomy Needle61. Double Neurectomy Tenaculum62. Adventitious Nerve-supply to Foot. (Sessions)63. Tip Shoe64. The Tip Shoe 'let in' to the Foot65. The Thinned Tip66. Drawing-knife for Charlier Shoeing67. The Foot prepared for the Charlier Shoe68. Bar Shoe69. Rubber Bar Pad on Leather70. The Bar Pad applied with a Half-shoe71. Frog Pad72. Frog Pad applied73. Smith's Expansion Shoe for Contracted Feet74. A Contracted Foot treated with Smith's Shoe75. De Fay's Vice76. Hartmann's Expanding Shoe77. 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-iron87. Sand-crack Forceps and Clamp. (Vachette's)88. McGill's Sand-crack Clamp89. Koster's Sand-crack Clamp90. Sand-crack Belt91. Method of 'Easing' the Bearing of the Wall on the Shoe in the Treatment of Sand-crack92. Method of 'Easing' the Bearing of the Wall on the Shoe in the Treatment of Sand-crack93. Method of 'Easing' the Bearing of the Wall on the Shoe in the Treatment of Sand-crack94 96. Grooving the Wall in the Treatment of Sand-crack97. Removing the Wall in the Treatment of Sand-crack98. Removing the Wall in the Treatment of Sand-crack99. 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 Shoe103. Three-quarter Bar Shoe104. Shoe with a 'Dropped' Heel105. Shoe with a 'Set' Heel106. Curette, or Volkmann's Spoon107. 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-shoe111. Toe of Hind-shoe Bevelled for the Prevention of Overreach112. 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 Cartilage143. 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, bearingtwo 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 offersthree surfaces,two lateral angles, andthree 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, thepreplantar groove, orpreplantar 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, theSemilunar 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, thePlantar Foramen. From this foramen runs thePlantar Groove, a channel, bounded above by the superior edge, and below by the semilunar crest of the bone, which conducts the plantar arteries into theSemilunar Sinus, a well-marked cavity in the interior of the bone. The Superior or Articular Surfaceconsists 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 Edgeof the laminal surface, describes a curve, with the convexity of the curve forward. In, outlining the superior margin the centre of the curve is a triangular process, thePyramidal 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 Anglesof the bone, also termed theWings, are two projections directed backwards. Each is divided by a cleft into an upper, theBasilar Process, and a lower, theRetrossal 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 Surfaceof 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 Surfaceresembles 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 Borderpossesses 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.