THE AKIMY ]IORSE. 47 



union between the horny and sensitive frog. The horny frog 

 serves to break the jar or eoneussion by acting as a cushion or 

 pad ; it protects the sensitive frog and prevents the foot from 

 slipping. 



Structure of horn. 



The horn of the hoof presents a fibrous appearance and con- 

 sists of very fine horn fibers or tubes, simihir to hairs, running 

 downward and forward and held together b}" a cementing sub- 

 stance. The horn fibers of wall, sole, and frog all run in the 

 same direction, downward and forward, the onl}^ difference 

 being that those of the frog are much finer and softer and run 

 in Avavy lines, whereas the fibers of wall and sole are straight. 



The horn fibers grow from the sn'tall villi, which cover the 

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



Circulation of Mood tlirough the foot. 



In j)revious study of the arteries we have seen that the lai^ge 

 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^ trans rerse, artery of the frog, 

 preplantar ungucd., and plantar ungual. 



The perpendicular artery is given off at right angles about 

 the middle of the os snffraginis, 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 comes 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 

 corona^. The deep coronary arch is the name given to this 

 arrangement of the arteries, and branches from this arch also 

 supply the coronary band. 



The artery of the frog rises behind the pastern joint at the 

 upper border of the lateral cartilage. It has two branches — 

 a posterior, which runs back and supplies the bulb of the heel, 



