44 THE ABMY HOBSE IN ACCIDENT AND DISEASE. 



The horny sole protects the sensitive sole and does not, in a healthy 

 foot, bear weight, except a very narrow border at the white line, an 

 eighth or tenth of an inch in width. 



The homy frog is the wedge-shaped mass of horn filling up the tri- 

 angular space between the bars. The lower face shows two prominent 

 ridges, separated behind by a cavity, called the deft, and joining in 

 front at the apex or point of the frog; these ridges terminate behind in 

 the bulbs of the frog. Between the sides of the frog and the bars are 

 two cavities, caUed the commissures. The upper surface of the horny 

 frog is the exact reverse of the lower and shows in the middle a ridge 

 of horn, called the frog stay, which assists in forming a firm union be- 

 tween the homy and sensitive frog. The homy frog serves to break 

 the jar or concussion by acting as a cushion or pad; it protects the 

 sensitive frog and prevents the foot from slipping. 



Structure of horn. 



The hom of the hoof presents a fibrous appearance and consists 

 of very fine hom fibers or tubes, similar to hairs, running downward 

 and forward and held together by a cementing substance. The 

 hom fibers of wall, sole, and frog all run in the same direction, down- 

 ward and forward, the only difference being that those of the frog 

 are much finer and softer and run in wavy Unes, whereas the fibers 

 of wall and sole are straight. 



The hom fibers grow from the small viUi, which cover the surfaces 

 of the coronary band, sensitive sole, and sensitive frog. 



Circulation of hlood through the foot. 



Tn previous study of the arteries we have seen that the large 

 metacarpal of the fore leg and the great metatarsal of the hind leg 

 each divides just above the fetlock into two branches. These 

 branches are called the external and internal digital arteries, one on 

 the inner and one on the outer side of the fetlock joint. They 

 follow the borders of the flexor tendons downward and terminate 

 inside of the wings of the os pedis. Each of the internal and external 

 digital arteries gives off five branches — the perpendicular, transverse, 

 artery of the frog, pre plantar ungual, and plantar ungual. 



The perpendicular artery is given off at right angles about the 

 middle of the os suffraginis, descends on the side of the pastern, 

 bends forward and joins with the artery of the same name from the 

 opposite side and forms the superficial coronary arch. From this 

 arch branches descend to the coronary band. 



The transverse artery conies off under the upper border of the lateral 

 cartilage, runs .forward, and joins its fellow from the opposite side 

 between the' extensor pedis tendon and the os coronse. The deep 



