394 .UNGULATA 



or pedal bone. There is also a much smaller second extensor on 

 the outer side of this in each limb, the lateral extensor of the 

 phalanges. In the fore leg the tendon of this muscle (which corre- 

 sponds with the extensor minimi digiti of man) receives a slip from 

 that of the principal extensor, and is inserted into the first phalanx. 

 In the hind leg (where it is the homologue apparently of the 

 peroneus brevis of man) the tendon becomes blended with that of the 

 large extensor. 



A very strong ligamentous band behind the metapodium, 

 arising from near the upper extremity of its posterior surface, 

 divides into two at its lower end, and each division, being first 

 connected with one of the paired upper sesamoid bones, passes by 

 the side of the first phalanx to join the extensor tendon of the 

 phalanges. This is called in veterinary anatomy the " suspensory 

 ligament of the sesamoids," or of the " fetlock " (10 in Fig. 164) ; but 

 its attachments and relations, as well as the occasional presence of 

 muscular fibres in its substance, show that it is the homologue of 

 the short flexor muscle of other mammals, curiously modified both 

 in structure and function to suit the requirements of the Horse's 

 foot. Behind or superficial to this are placed the two strong tendons 

 of the long flexor muscles, the most superficial, or flexor perforatus 

 (8), dividing to allow the other to pass through, and then inserted 

 into the middle phalanx. The flexor perforans (9) is as usual in- 

 serted into the terminal phalanx. In the fore leg these muscles 

 correspond with those similarly named in man. In the hind leg, 

 the perforated tendon is a continuation of that of the plantaris, 

 passing pulley -wise over the tuberosity of the calcaneum. The 

 perforating tendon is derived from the muscle corresponding with 

 the long flexor of man, and the smaller tendon of the oblique flexor 

 (tibialis posticus of man) is united with it. 



The hoof of the Horse corresponds to the nail or claw of other 

 mammals, but is so constructed as to form a complete and very 

 solid case to the expanded termination of the toe, giving a firm 

 basis of support formed of a nonsensitive substance, which is con- 

 tinually renewed by the addition of material from within as its 

 surface wears away by friction against the ground. The terminal 

 phalanx of the toe is greatly enlarged and modified in form to sup- 

 port this hoof, and the size of the internal framework of the foot is 

 further increased by a pair of lateral fibro- cartilaginous masses 

 attached on each side to the hinder edges of the bone, and by a 

 fibro-cellular and adipose plantar cushion in the median part. 

 These structures are all enclosed in the keratogenous membrane or 

 " subcorneous integument," a continuation of the ordinary derma of 

 the limb, but extremely vascular, and having its superficial extent 

 greatly increased by being developed into papillae or laminae. From 

 this the horny material which constitutes the hoof is exuded. A 



