HORSESHOEING. 45 



the fleshy sole, it has much finer and shorter villi and contains 

 fewer blood-vessels. It secretes the soft, horny frog. 



(c) The horn capsule or hoof (Fig. 26) is the entire mass made 

 up of the horn-cehs secreted from the whole surface of the podo- 

 derm, and next to the shoe is the organ with which the horse- 

 shoer has most to do. The horn capsule or hoof is nothing more 

 than a very thick epidermis that protects the horse's foot, just as 

 a well-fitting shoe protects the human foot. The hoof of a sound 

 foot is so firmly united with the underlying pododerm that only 

 an extraordinary force can separate them. In its normal condi- 

 tion the hoof exactly fits the soft structures within it ; hence it is 

 evident that local or general contraction of the hoof must pro- 

 duce pressure on the blood-vessels and nerve-endings of the 

 pododerm, disturb the circulation of the blood and the nutrition 

 of the foot, and cause pain. 



The hoof is divided into three principal parts, which are 

 solidly united in the healthy foot, — namely, the wall, the sole, 

 and the frog. That part of the hoof which is almost wholly 

 visible when the foot is on the ground (Fig. 26, 6, c), and which 

 protects the foot in front and upon the sides, is known as the 

 wall. In position, course, direction, and arrangement of its 

 parts it simulates the different parts of the pododerm from 

 which it is developed. It extends from the edge of the hair just 

 above the coronary band to the ground ; backward it gradually 

 decreases in height (length), passes around the bulbs of the heels, 

 and turns forward and inward (Fig. 28, a, 6) to form the bars, 

 which are finally lost in the edge of the sole near the summit of 

 the frog. It thus forms at each heel an angle (Fig. 27, d) known 

 as a buttress, which encloses a branch of the horny sole. Exter- 

 nally the wall is smooth, covered with the varnish-like periople, 

 and presents indistinct ring-like markings (Fig. 26). Its inner 

 surface, on the contrary, presents a great number of horn-leaves 

 which are spoken of collectively as the keraphyllous tissue 

 (Fig. 29, /). The upper or coronary border of the wall is thin 

 and flexible, and on its inner aspect is the coronary groove, into 



