THE NERVOUS SYSTEM 169 



ris, but superficial to the M. caput longum musculorum contrahen- 

 tium. When it arrives at the mesial edge of the latter muscle, at 

 about the level of the middle of the fore-arm, it gives two muscular 

 branches. The smaller of these divides into three to supply the M. 

 flex. prim. comm. and the MM. flex, antibr. et carpi ulnaris and 

 radialis. The other branch R. medianus (Ribbing) = R. superficialis 

 medialis, McMurrich (n.ul.r.m.), passes along the mesial edge of 

 the M. cap. long. muse, contra., and appears to terminate at the 

 point where the M. flexor accessorius medialis joins the tendon of the 

 M. flex. prim. comm. It innervates the M. cap. long. muse, contra, 

 and the M. flex. ace. med. 



The main N. ulnaris, after giving off the R. medianus crosses the 

 ulna, and, following the mesial border of the M. flex carpi ulnaris, 

 emerges at the side of the arm between this muscle and the M. flex. 

 ace. lat. At the proximal border of the M. flex. ace. lat. a twig enters 

 the muscle, and as the nerve passes along its lateral border a fairly- 

 constant branch is given off to the skin. At the base of the fourth 

 digit another cutaneous branch passes along the ulnar side of the 

 finger, while the main nerve turns mesially again and crosses the 

 base of the finger, between the MM. eontrahentes digitorum and 

 the M. flex. brev. prof. IV to the interdigital space of the third and 

 fourth digits. Here it divides again into three main branches, of 

 which two are distributed to the skin of the adjoining sides of the 

 third and fourth fingers, while the remaining one crosses the base of 

 the third digit, between the M. contra, digit, and the M. flex. brev. 

 prof. Ill, to join the corresponding palmar branch of N. interosseus. 

 Besides these cutaneous branches a number of small muscular 

 twigs may be traced into the several short flexor muscles of the 

 fourth digit, e.g. M. contra, digit., M. flex. brev. super, and prof., 

 M. flex, digit, min., and M. interossei III-IV. 



A^. interosseus (n.io.). Ribbing (1907). 



R. profundus ...... McMurrich (1903). 



N. medianus ....... Sieglbaur (1904). 



This branch almost immediately dips down to the dorsal side of 

 the M. interosseus antibrachii, and passes alongside the extensor 

 nerves — NN. dors, manus inter, and ulnaris — in the interosseal 

 space of the radius and ulna. It lies anterior — radial — to the 

 N. dors, manus inter. There is no anastomosis between these nerves 

 in the Salamander as there is in Triton (cf. Sieglbaur, 1 904). During 

 its course down the fore-arm it gives one or two twigs to the M. 

 interosseus antibrachii, and also to the M. pronator profundus. The 



