618 



COMPAEATIVB PHYSIOLOGY. 



terminations of the common extensor and the perforans ten- 

 dons ; the lateral cartilages ; a certain amount of connective 

 and fatty tissue ; the hoof -secreting mechanism, together "with 

 the hlood-vessels, nerves, lymphatics, etc., essential for all parts. 



The relative size and position of parts may he gathered from 

 the accompanying cuts. The lateral cartilages belong to the 

 class known as flbro-cartilage, acting, no doubt, as perfect 

 bujEfers ; and as springs must be of no small assistance in loco- 

 motion. 



The homy matter of the foot (hoof) owes its formation to 

 the cells of a tissue bearing various names in different regions. 



h J k 



Fie. 466. 



Fio. 465.— Plantar or ground surface of a hoof; right foot. The interval from a to a 

 represents the toe; from a to 6, b, ontside and inside quarters; c, o, commence- 

 ment of bars; d, d, inflexions of wall at heels or " buttresses "; e, lateral lacuna; 

 f,f f, sole; g, white line; g", ditto, between sole and bar; h, body of frdg; i, 

 branch of frog; k, k, glomes, or heels of frog; I, median lacuna. 



Fig. 466. — Horn cells from sole of hoof, a, young cells from upper surface of sole; 

 ft, cells from lower surface, or dead horn of sole. 



but consisting of a basis of- fibrous tissue abounding in blood- 

 vessels and nerves. The vessels from their arrangement have 

 determined the names given to the formative tissue, such as 

 villosities, villi, velvety tissue, vascular laminae, etc. It can not, 

 however, be too well borne in mind that these structures are 

 after all, only modified corium (Fig. 371). 



Just as the epidermis, with its numerous layers, arises from 

 a modification of cells in the lower layers, resting on the vascu- 

 lar villi of the corium, so the hoof owes its origin to a similar 

 source. Thus from the velvety tissue is formed the sole and 

 frog ; from the perioplic ring, the periople; and from the coro- 

 nary cushion, the wall (see figures). 



