DISSECTION OF THE ANTERIOR LIMB. 29 



^ving of the os pedis, where it bifurcates to form the plantar and pre- 

 plantar arteries. Each artery is related in front to the vein of the 

 same name, and behind to tlie posterior branch of the plantar nerve. 

 The anterior branch of the same nerve crosses the vessel at the 

 fetlock ; while other twigs cross over the artery and form the 

 middle branch, which will be found between the artery and vein, or 

 resting on the former. Crossing these vessels and nerves obliquely, 

 is a small glistening ligamentous cord (Plate 9) which stretches 

 downwards and forwards from the horny spur behind the fetlock, 

 becoming attached within the wing of the os pedis. A knowledge of 

 these relationships is of importance for the performance of the lower 

 operation of neurectomy. The collateral branches of the digital 

 arteries are : — 



1. At different levels numerous small branches for the skin, tendons, 

 or articulations. Among these may be included the rameaux echelonnes 

 of Bouley (Plate 10). These branches, some of them of considerable 

 size, spring from the posterior aspect of the artery, and anastomose 

 across the back of the digit with corresponding branches from the 

 opposite side, forming arches arranged like the steps of a ladder. 



2. The Perpeiidicular Artery, which comes off at a right angle about 

 the middle of the first phalanx, and divides almost immediately into an 

 ascending and a descending set of branches, both of which are distri- 

 buted on the front of the first phalanx. Branches from each of these 

 sets anastomose with corresponding vessels from the opposite side. 



3. The Artery of the Plantar Cushion. 



4. Vessels forming the Coronary Circle. 



The last two, as well as the terminal branches of the digital arteries, 

 will be described in connection with the foot. 



The Small Metacarpal Artery (Plate 9). This, the smaller 

 terminal branch of the posterior radial artery, descends behind the 

 carpus and towards its inner side. It is superficially placed to the 

 fibrous band completing the carpal arch, while the large metacarpal 

 lies beneath that structure. In company with it is the first part of 

 the median vein. At the level of the head of the inner metacarpal 

 bone it crosses to the outer side by passing between the suspensory 

 lio-ament and the subcarpal ligament, or check-band furnished from the 

 back of the carpus to the tendon of the deep flexor. It here anasto- 

 moses with a branch already described as descending from the supra- 

 carpal arch. In this way the subcarpal arch is formed. 



The Subcarpal or Deep Palmar Arch gives off the following two 

 pairs of arteries : — 



1 The Anterior or Dorsal Interosseous Metacarpal Arteries. — These 

 are small vessels (Plate 9), one on each side of the limb, which turn 

 forward round the heads of the small metacarpal bones, and descend in 



