REGIONAL ANATOMY 23 
shall be afterwards concerned with it in the operation of 
neurectomy. Its point of origin is the inside of the inferior 
extremity of the radius. Descending in company with the 
flexor tendons, and passing behind the carpus and beneath 
the carpal sheath, it continues its descent, in company with 
the internal plantar nerve and the internal metacarpal vein, 
on the inner side of the flexor tendons until just above the 
fetlock. At this point it bifurcates into the digital arteries. 
From the carpus downwards the large metacarpal artery, 
the internal metacarpal vein, and the internal plantar nerve 
are in close relation with each other. The vein holds the 
anterior position. The artery is between the two, and has 
the nerve in close contact with it behind. 
Tue Drerran ARTERIES, OR COLLATERAL ARTERIES OF THE 
Die1r.—These are of large volume, and carry the blood 
to the keratogenous apparatus of the foot. They separate 
from each other at an acute angle, and pass over the side of 
the fetlock, one to the inside, the other to the outside, 
to reach the internal face of the basilar process of the 
os pedis, where they bifurcate to form the Plantar and 
Preplantar arteries. In the whole of their course the digital 
arteries follow the flexor tendons, and are related in front 
to the digital vein, and behind to the posterior branch 
of the plantar nerve. This is the nerve implicated in the 
lower operation of neurectomy, and its relation to adjoining 
structures will be detailed under Section F. of this chapter. 
During its course the digital artery gives off branches in 
the following positions : 
1. At the Fetlock numerous branches to the metacarpo- 
phalangeal articulation, the sesamoid sheath, and the 
tendons. 
2. At the Upper Extremity of the First Phalanx branches 
for the supply of the surrounding tissues, and for the tissues 
of the ergot. 
3. Towards the Middle of the Third Phalanz, the Perpen- 
dicular artery of Percival. This arises at a right angle 
from the main vessel, and immediately divides into two 
series of ramifications—an ascending and a descending. 
