866 THE NERVES. 



14. Median or Cubito-plantar Nerve (Fig. 465, 20). 



This nerve is composed of fibres coming from the dorsal and eighth cervical 

 pairs. It is detached from the posterior part of the trunk of the plexus and 

 proceeds towards the axillary artery, where it forms an anastomosis with the 

 anterior brachial nerve, through the loop already noticed when describing that 

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



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

 panies 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 lies against the internal 

 ligament of that joint, and crosses — at a very acute angle — the direction of its 

 satelUte vessel to become posterior. This position it inverts below the articu- 

 lation, 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 forearm, 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 passing to the anterior 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 forearm. This branch enters beneath the biceps, 

 and forms two divisions ; one of these is expended in the brachialis anticus 

 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 forearm to below the carpal region (Fig. 465, 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 large metacarpal artery, 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 ramuscules, and an anasto- 

 mosing 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 accom- 

 panies the external metacarpal vein 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. Con- 



