SOLIPEDA. 



741 



ral boundary and form to the lateral, the pos- 

 terior, and inferior parts of the foot ; and 

 when the bars or frog are thrust upwards by 

 pressure from without, they are then acting 

 against this same horizontal flooring, formed 

 by the cartilage and the frog, and met by the 

 depression of the bones of the foot forced 

 down from the weight of the animal ; the 

 whole can then dilate exteriorly along with 

 the posterior and more elastic parts of the 

 hoof. 



Fig. 515. 



Longitudinal Section of the Foot of the Horse. 



1, Great pastern bone ; 2, lesser pastern or coro- 

 nary bone ; 3, sesamoid bone implanted in the flexor 

 tendon of the last phalanx ; 4, coffin bone ; 5, tendon 

 of extensor digiti ; 6, tendon of flexor sublimus ; 7, 

 tendon of flexor profundus ; 8, section of the posterior 

 expansion of the great cartilage ; 9, soft cushion of 

 the heel ; 10, section of horny hoof; 11, sensitive 

 hoof; 12, anterior section of the cartilage spreading 

 over the coffin bone. 



The objects attained by the introduction of 

 this admirable structure into the foot of the 

 soliped are various, and have been well pointed 

 out by Bracy Clark, in his excellent treatise, 

 to which we must refer the reader for many 

 practical applications connected with the 

 veterinary art, that would be foreign to the 

 objects of the present article. First, seeing 

 that the resistance of a solid unyielding sup- 

 port would have been inadmissible, the pedal 

 cartilages are employed as a substitute for 

 bone, and made to occupy a very large share 

 in the composition of the hinder part of the 

 foot ; for it will be remarked, the coffin bone, 

 except by its extremity, does not extend be- 

 yond the middle of the hoof (./%. 515.), the 

 posterior shape of the foot being almost wholly 

 communicated by the cartilage, which, passing 

 nearly around the whole coronary circle, serves 

 to support and convey the skin to its lodg- 

 ment in the coronary concavity of the hoof. 

 Secondly, it serves to equalise the pressure 

 every where over the internal surface of the 

 hoof when under the pressure of the weight 

 from within, during the descent of the bones 



of the foot, and, what is singular, the hoof 

 itself is the most solid material of these hind 

 parts of the foot. 



A more important office still remains to 

 be explained, namely, that of supplying the 

 coffin bone with a considerable share of its 

 capability of motion in the interior of the 

 hoof; for it is to be remarked that, as the 

 coffin bone is obliged to describe in its de- 

 scent a small portion or segment of a circle, 

 at its back part, round its centre of motion, 

 or rather its more fixed part (for there is 

 none of it wholly fixed), towards the front of 

 the foot ; so this could not so well have been 

 accomplished had the bone itself been fixed 

 at its upper part to the processes in front of 

 the hoof, these being too inconsiderable to 

 afford, in that part of the bone, the extent of 

 motion required ; but, by the intervention of 

 an elastic cartilage between the bone and the 

 substance of the hoof, the bone acquires 

 greater liberty for action, and movement of 

 its upper parts. 



The cartilages of the foot, in old horses, 

 not unfrequently become partially ossified, in 

 which condition they are known to farriers by 

 the name of ring-bones. 



Soft Parts of the Foot. On removing the 

 hoof, and its horny appendages situated be- 

 neath the sole of the foot, the whole subjacent 

 surface is found to consist of a thick, villous 

 looking, and highly vascular membrane, 

 moulded exactly to its inner surface, to which 

 the name of sensitive foot is generally applied ; 

 or, according to the structures beneath which 

 it is situated, it is sometimes divided into 

 sensitive hoof, sensitive frog, &c. This struc- 

 ture is, indeed, the matrix from which the 

 entire corneous hoof derives its origin, and 

 is essentially similar, in its texture and func- 

 tions, to the soft core upon which the hollow 

 horns of many ruminants and the vascular 

 secreting surfaces upon which the nails and 

 claws of unguiculate quadrupeds are formed. 

 Externally it presents, upon the anterior sur- 

 face of the foot, the broad vascular laminae 

 which interdigitate with the horny plates, pro- 

 jecting from the interior of the hoof, as de- 

 scribed above, so as to amplify, to a very 

 considerable amount, the extent of surface 

 whereby the contact between the sensitive 

 foot and the wall is effected. 



This entire surface is richly supplied with 

 nerves and bloodvessels, the latter of which 

 open into capacious plexuses, that surmount 

 the coronary margin of the hoof (Jig. 514.), 

 and, when injected, present a very beautiful 

 appearance. 



NERVOUS SYSTEM AND ORGANS OF THE 

 SENSES. The general arrangement of the 

 nervous system and structure of the organs of 

 sensation offer in the class before us no pecu" 

 liarities of sufficient physiological importance 

 to require a detailed description : we append, 

 however, figures representing the cerebral con- 

 volutions and the base of the encephalon of 

 the horse for comparison with similar figures 

 given in other articles. 



SB 3 



