1894.] AiTATOMX OP ATHEETTBA ATEICAXA. 689 



The median nerve rises from the 6th, 7th, and 8th C. and 1st D. 

 In the lower third of the arm it gives off a large branch to supply 

 the outer side of the forearm as far as the dorsum of the hand. 

 Just below this twigs are given off to the bracliialis anticus, after 

 which the nerve enters the forearm and supplies all the flexor 

 muscles except the flexor carpi ulnaris, but there is no definite 

 anterior interosseous nerve. In the hand the median supplies the 

 thumb-muscles and the skin of the palmar surface of all the 

 lingers. 



The musculo-spiral derives fibres from all the roots forming the 

 brachial plexus ; it winds round the back of the humerus, 

 supplying the triceps, dorso-epitrochlearis, and skin of the upper 

 arm, but I was unable to find any branch going into the brachialis 

 anticus. Just above the elbow it divides into radial and posterior 

 interosseous ; the former runs through the substance of the 

 extensor carpi radialis longior, supplying it and the brevier, after 

 which it is continued down to the back of the hand to supply the 

 skin of the dorsum of the radial three and a half fingers. The 

 posterior interosseous passes deep to the supinator brevis and 

 breaks up into a brush of nerves for the extensor muscles. 



The ulnar nerve rises from the 8th C. and 1st D. and runs 

 down behind the internal condyle, supplying the epitrochleo- 

 anconeus, flexor carpi ulnaris, and palmaris brevis, but not the 

 flexor profundus digitorum. In the hand it supplies all the deep 

 muscles of the palm but no skin. Before it reaches the \rast a 

 dorsal cutaneous branch is given off, which supplies the skin of 

 the back of the ulnar one and a half fingers. 



The internal cutaneous nerves come from the 1st D. and supply 

 the skin of the inner side of the arm and forearm. 



The anterior thoracic nerve rises from the Sth C. and 1st D., 

 and is one of the largest nerves in the plexus ; it supplies the 

 pectoral muscles and the ventro-lateral part of the panniculus. 



The posterior thoracic nerve comes from the 7th C. and runs 

 back behind the plexus to supply the serratus magnus. 



I am not certain of the origins of the nerves to the teres major 

 and latissimus dorsi. The former does not supply any of the sub- 

 sea pularis. 



The lumbar plexus is formed by the 2nd, 3rd, and 4th lumbar 

 nerves. The first lumbar is quite separate and runs round the 

 body-walls after the manner of the intercostal nerves ; it divides 

 into two branches, which probably correspond to the ilio-hypo- 

 gastric and ilio-inguinal nerves of human anatomy. 



The genito-crural nerve rises from the 2nd L. and appears on 

 the surface of the psoas magnus, after which it crosses the tendon 

 of the psoas parvus from within outwards ; it then runs back to 

 supply the skin over the region of the groin, I failed to notice 

 any branches going to the muscular wall of the inguinal pouch. 



The external cutaneous nerve comes from the 2nd and 3rd L. 

 and appears on the surface of the psoas magnus external to the 



Pboc. Zool. Soc— 1894, No. XLVI. 46 



