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. 



The Digital Arteries, or Collateral Arteries of the 

 Digit. — 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 wdiole 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 Phalanx, the Per- 

 pendicular 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. 



