THE BRACHIAL PLEXUS. 761 



the anterior brachial nerve, through the loop already noticed when describins 

 that nerve as being formed by filaments passing from one cord to the other 



Leaving this point, it is placed in front of the humeral artery and 

 accompanies it to its terminal bifurcation ; then it continues to descend on 

 the inner face of the limb, along with the principal branch of that artery— 

 the posterior radial— until it reaches the ulnar articulation, where it responds 

 to the internal ligament of that joint, and where it crosses, at a very 

 acute angle, the direction of its satellite vessel to become posterior. This 

 position It inverts below the articulation, when it assumes, and preserves for 

 the greatest part of its extent, its antibrachial course, remaining always a 

 little more superficial than the artery. Above the lower third of the fore- 

 arm, it bifurcates to form the plantar nerves. 



In its course, this nerve successively furnishes : 



1. Before its arrival on the axillary artery, one of the originating 

 branches of the thoracic nerve destined to the superficial pectoral muscle. 



2. At the middle of the humerus, a long branch, represented in Man by 

 that portion of the musculo-cutaneous nerve which proceeds to the anterior 

 brachial muscle and the skin of the fore-arm. This branch enters beneath 

 the coraco-radialis or biceps, and forms two divisions ; one of which is 

 expended in the short flexor of the fore-arm; while the other passes 

 between that muscle and its congener, the long flexor, to become superficial 

 and gain the internal aspect of the limb, when it breaks up into two 

 principal filaments, which pass to the external face of the antibrachial 

 aponeurosis, and accompany with their divisions the two subcutaneous 

 veins of the fore-arm to below the carpal region (Fig. 347, 21, 22). 



3. In the antibrachial region, and at various elevations, but particularly 

 below the ulnar articulation, ramifications to the internal flexor of the 

 metacarpus and the two flexors of the phalanges. 



Plantar Nerves. — These nerves, two in number, are distinguished as 

 internal and external. 



The internal plantar nerve, one of the terminal branches of the median 

 nerve, lies beside the collateral artery of the cannon, and follows that vessel 

 along the perforans tendon to near the fetlock, where it ends in several 

 digital branches. In its track it furnishes a number of cutaneous metacarpal 

 ramusoules, and an anastomosing branch, which, after being detached from the 

 principal trunk, about the middle of the cannon, bends obliquely behind the 

 flexor tendons to join the external plantar nerve. This is formed by the 

 union of two branches : one coming from the ulnar nerve, the other from 

 the median, and joining the first at the upper border of the pisiform bone, 

 after passing beneath the inferior extremity of the oblique flexor of the 

 metacarpus. This nerve, which accompanies the external collateral vein of 

 the cannon for its entire length, descends with it, and with an arteriole that 

 concurs in forming the subcarpal arch, outside the flexor tendons, in a 

 special fibrous channel of the carpal sheath'. Near the superior extremity of 

 the cannon, within the head of the external metacarpal bone, it sends on 

 the posterior face of the suspensory ligament of the fetlock a deep plantar 

 branch, chiefly destined to the fleshy portion of the interosseous muscles. 

 It is the analogue of the deep palmar branch of the ulnar nerve in Man. 

 Continuing its descending course along the perforans tendon, it throws off 

 some superficial metacarpal ramuscules, receives the accessory branch 

 supplied by the internal nerve, and terminates, like the latter, in a number 

 of digital branches on arriving at the fetlock ; these it now remains for us 

 to examine. 



