CHAPTER IV. 

 ANATOMY AND PHYSIOLOGY OF THE HORSE'S FCCT. 



26. By anatomy of the foot is meant a description of the various 

 parts entering into its formation, and by physiology is meant the 

 functions or uses of these parts. 



27. The horse's foot is composed of four parts —the bones, the 

 elastic structures, the corium, and the outer protective covering of 

 horn, called the hoof, which incloses and protects the other parts. 



28. The bones of the pastern region and foot form a column ex- 

 tending downward from the fetlock into the hoof. They are the 

 first phalanx (long pastern bone), extending from the fetlock joint 

 to the pastern joint; the second phalanx (short pastern bone), ex- 

 tending fi-om the pastern joint to the coffin, or pedal, joint ;^ the third 

 phalanx (coffin bone) and the navicular hone (distal sesamoid). (See 

 PL IV.) 



The third phalanx (coffin bone) is of irregular shape, is situated 

 within the hoof, and is similar to the hoof in form. The surface of 

 the front and sides is known as the wall surface. It has a number of 

 small openings for the passage of blood vessels and nerves, and is 

 roughened to give attachment to the laminar corium which covers 

 it. At the top of this surface, in front, is a projection called the 

 extensor process, to which is attached the common digital extensor 

 tendon (common extensor of the fooi). On each side of the coffin 

 bone is an extension to the rear called the wing. The lateral car- 

 tilages are attached to the outer and upper borders of the wings and 

 the ends of the naxdcular bone are attached to the inner surfaces. 



The lower surface of the coffin bone, called the sole surface, is con- 

 cave, half-moon shaped, and smooth, except at the back part, which 

 is roughened for the attachment of the tendon of the deep flexor of 

 the foot. It is called the tendinous surface. The upper surface, 

 called the articular surface or joint surface, articulates with the second 

 phalanx and na\icular bone, and with them forms the coffin joint. 



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