28 THE SURGICAL ANATOMY OF THE HORSE 



The Subscapular Nerve (5). — The fibres of this nerve come from the 

 cervical roots of the plexus. The nerve appears in the plate beneath 

 the posterior border of the fasciculus, and runs upwards on the face of the 

 subscapularis muscle, which it supplies by splitting up into a number of 

 filaments. 



T/ie Ulnar Nerve (28). — Owing to the pinning down of the plexus 

 the latter has been flattened out, with the result that the ulnar nerve is 

 displaced in the backward direction. Instead of being placed in front of 

 the musculo-spiral nerve (which it separates from the axillary vessels), as 

 when the plexus is in the ordinary position, it runs down behind it. Its 

 fibres are derived from the dorsal roots of the plexus, and the nerve runs 

 down the limb behind the axillary and brachial vessels. In the plate it 

 is observed to run along the cut anterior edge of the scapulo-ulnaris 

 muscle. 



As we approach the elbow the ulnar nerve deviates backwards, 

 receding from the brachial vein, and disappearing beneath the scapulo- 

 ulnaris muscle to gain the inner aspect of the olecranon process of the 

 ulna. 



Just above the carpus the nerve is again visible in the plate, where 

 its terminal branch (44) is seen to pierce the fibrous arch of the knee 

 and unite with a branch from the median nerve (40), thus forming the 

 external plantar nerve, which quickly disappears in the fibrous tissue. 



The Median Nerve (21). — This nerve arises by two roots. The fibres 

 of the anterior root (13) are derived from the sixth, seventh, and eighth 

 cervical nerves, whilst those of the posterior root (15) come from the 

 eighth cervical and first dorsal. The roots so formed unite, and in the 

 loop between them the axillary artery rests. The median nerve (21) 

 then takes a downward course in front of the axillary artery, and 

 subsequently in front of the brachial artery, with which it crosses 

 the shaft of the humerus obliquely. It then follows the posterior 

 radial division of the brachial artery, being at first in front of this 

 vessel. On the inner aspect of the elbow it crosses the artery, and 



