THE NERVOUS SYSTEM 167 



arm, and then passes round under the M. extensor antibr. et carpi 

 ulnaris — i.e. between this muscle and the ulna — into the interosseal 

 space of the fore-arm. In doing so it supplies one or two twigs to the 

 above-named muscle and finally gives a large anastomosis — amount- 

 ing almost to the entire nerve in some cases — to the N. dorsalis manus 

 ulnaris. The remainder of the nerve ends in the MM. extensores 

 antibr. et carpi radialis and ulnaris. 



The exact relation between the NN. extensorius caudalis and 

 cranialis at this point is subject to some variation. In one case no 

 certain anastomosis between these nerves in the fore-arm could be 

 found. In this example both nerves were approximately equal in 

 size all the way along, and the anterior nerve did not divide in the 

 fore-arm but formed only the N. dors, manus inter., while the 

 posterior nerve ran parallel with it and formed the N. dors, manus 

 ulnaris. If any fusion between these nerves occurred at all it was at 

 the elbow-joint, in a similar position to that described by Sieglbaur 

 (1904) for Necturus, but owing to the ribbon-like, translucent 

 appearance of the nerves in this specimen, it was impossible to 

 decide whether one was dealing with a nervous connexion or merely 

 with the connective tissue capsule of the joint. In any case the 

 anastomosis, if it did occur, was very fine and in no way comparable 

 with the normal condition described above. 



Flexor nerves. 



N. brachialis (n.br.). 



N. brachialis longus inferior .... Furbringer (1873}. 

 After receiving the anastomosis from the third nerve, N. spinalis 

 4 gives off posteriorly N.pectoralis (n.pect.) to the pectoralis muscle. 

 The N. pectoralis passes round the posterior border of the coracoid 

 and enters the muscle on its mesial side. It is accompanied by a 

 cutaneous nerve which supplies the skin covering the pectoral 

 region. From about this level another cutaneous nerve arises, N. 

 cutaneus brachii superior medialis (n.cut.br.s.m.) (42, Fiir.), supplying 

 the skin of the axilla, and the postero-mesial aspect of the upper 

 arm. 



After giving off these branches, the brachial nerve (which forms the 

 main continuation of the fourth spinal nerve) enters the arm ventral 

 to the extensor nerves, posterior to the shoulder-joint, and between 

 the M. anconaeus coracoideus and the M. anconaeus scapularis 

 lateralis, and passes to the ventral side of the humerus. It then 

 divides into a R. superficialis and a R. profundus (Furbringer), 



