CHAPTER XVII 



THE FOOT 



Horns, nails, claws, and hoofs represent a modified form of 

 epithelium, and the surface from which these are secreted 

 corresponds to the deep layers of the skin. The other horny 

 structures found connected with the skin of the horse — i.e., the 

 chestnuts and ergots — have a similar origin. Considered by itself, 

 a piece of horn, a claw, or nail, would not appear to possess any 

 special physiology ; but once the nail surrounds and completely 

 encloses the end of the limb, as it does in the ungulata, a special 

 physiology arises, and this reaches its highest development in 

 the solid-footed horse. The foot in this animal has become a 

 highly specialised structure, for the purpose of resisting wear 

 and tear, for supporting the weight of the body, and in saving the 

 foot and limb from concussion. If it were merely a block of 

 horn on which the horse stood, it would offer nothing of special 

 interest. 



A foot consists of three feet, each enclosed within the other. 

 Externally there is the hoof or horn-foot ; within this is a complete 

 counterpart in fibrous and vascular tissue known as the sensitive 

 foot, and the latter is moulded upon a bony structure which in 

 appearance resembles a miniature foot. It is usual, however, 

 to regard the foot as being divided into two portions, an in- 

 sensitive and sensitive, or an external and internal, the latter 

 term comprising both the vascular and the bony foot. The 

 internal and external feet are an exact counterpart of each other, 

 the former being on a smaller scale, to enable it to fit into the 

 external foot in the same way as a finger fits into a glove. 



The external and internal feet are not independent of each 

 other — one is the complement of the other. The external does 

 not produce itself ; it is dependent entirely on the internal for 

 every horn cell it possesses. The internal foot cannot tolerate 

 pressure, not even touch ; it is dependent on the external foot, 

 for the circumstance that, in spite of its highly sensitive 

 nature, it is throughout the life of the animal enabled to be 



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