THE FOOT. 27o 



PART X.— SPECIAL ANATOMY. 



The Foot. 



CoN^siDERED zoologically tlie foot of the horse compre- 

 hends all those structures placed below the inferior ex- 

 tremity of the tibia ; the point of os calcis corresponds to 

 the heel of the human subject. From the tarsus the 

 metatarsals run downwards ; their normal number in mam- 

 malia is five, in the horse, however, we find but three, for 

 the inner digit is absent and the two central ones coalesce. 

 The outer of the three in the fossil forms of the horse 

 present hoofs, and other structures found in the existing 

 forms only in connection with the double central digit. In 

 some cases even in the present day, however, we find a 

 rudimentary hoof produced below one of the metacarpal 

 or metatarsal splint bones, in rare cases ; generally these 

 bones terminate inferiorly in a slight bulbous enlargement. 

 It is, then, with the double central digit we have here to 

 deal ; its comj^osition of two similar parts is shown by its 

 symmetry, and by a depression well marked in some cases 

 at the antero- inferior part of the toe of os pedis. Again, 

 in all cases the frog is divided into two similar portions by 

 a deep fissure, the cleft, and often we see a projection on 

 the inner surface of the hoof opposite the depression in 

 the toe of os pedis just at the point of junction of the 

 wall and the sole of the hoof. That portion commonly 

 known as the foot, consists of a horny box with its con- 

 tents. The horny box corresponds to the nail of the toe 

 of the human subject with the thickened skin on the sole 

 of the foot, while the contents comprise certain bones with 

 their appendages covered by a layer of highly vascular 

 tissue, which corresponds to the true skin, and which pro- 

 duces the horn, which is analogous with the epidermis or 

 cuticle. The HOOF is separable from the other structures 

 by maceration by a continuation of this process it may be 



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