THE AKMY IIOKSE. 49 



Nerves of the foot. 



The nerves of the foot supply feeling: or the sense of touch 

 to the parts. The large nerve cortl on either side of the limb 

 divides at the fetlock joint into three branches, called the 

 dijiital nerves— the anterior, the posterior, and the middle. 



The anterior digital nerve passes downward and foi-ward 

 and supplies the anterior or front part of the foot. 



The jiosterior digital nerve, the largest of the three, passes 

 down behind the digital artery to supply the structures in the 

 posterior part of the foot. It gives off a branch which passes 

 through the notch in the wing of the os pedis (in company 

 with the preplantar ungual artery) to supply some of the 

 sensitive lamime; it also sends branches into the os pedis with 

 the plantar ungual artery. 



The middle branch is very small, is said to always join the 

 anterior l)ranch. and supplies the sensitive sole and fetlock 

 pad. 



The functions of most of the parts of the foot have been 

 mentioned in passing, but there are some points in connection 

 with the physiology of the foot which need to be explained 

 more in detail. 



Exjmnsion and contraction. 



When weight comes upon the leg. the os pedis descends 

 slightly and causes the sole to d^'scend and flatten. The plantar 

 cushion and horny frog are compressed between the ground 

 below and the structures above: this compression causes them 

 to spread out sidewise, carrying outward the lati'ral cartilages 

 and bars and the wall at the quarters. This is called expansion. 

 When weight is removed from the leg. the plantar cushion 

 becomes thicker and narrower, and the lateral cartilages and 

 quarters move inward to where they were before expanding. 

 This is called contniction. The elastic lateral cartilage is 

 mei-ely a ilexible extension of the Aving of the os pedis and 

 would appear to have been specially designed for expansion 

 and contraction at the ([uarters. It is also to be noted that the 

 bars arc a i)rovi>ion for this >anic purpose, since expansion and 

 contraction could not take place if the wall formed a solid 

 unbroken ring around the hoof. 



In addition to breaking the jar when the foot comes to the 

 LH-ound. the jdantar cushion has anothei- important use. It 



