THE SPINAL NÎJRVES. 187 



smaller terminal branch, supplies a branch to the M. extensor digit, 

 comm. longus and the skin over the carpus [Ramus cutanens inferior^ 

 re), and ends on the muscles of the little fing-er as the H. dorsalis 

 digiti V medialis. 



e. The R. radialis lateralis (R), the larger of the two branches, 

 supplies the extensor muscles of the fingers and gives bifurcating 

 branches, Rami digitales dorsales, to the adjacent sides of the second, 

 third, fourth, and fifth fingers (the Ramus dorsalis lateralis of the 

 second finger is supplied by the iV^ îdnaris). 



3. The third spinal nerve [N. sjjiualis III) (Fig. 122 Sill) leaves 

 the vertebral canal by the foramen between the third and fourth 

 vertebrae, and runs outwards and forwards upon the large transverse 

 process of the third vertebra to the brachial nerve [N. spinalis II). 

 Its behaviour at this point is subject to considerable variation ; at 

 times it joins the brachial nerve completely, at other times the two 

 nerves are simply in contact ; or lastly, it may send a small twig 

 to the brachial nerve. Externally to this point the two nerves 

 supply a number of small branches, which may belong almost en- 

 tirely to either one nerve or the other ; these nerves again inosculate 

 in a variable manner, to form an axillary plexus. The more con- 

 stant branches are : — 



(i) One or more twigs to the Muse, transverso-scajmlaris major. 



(2) Several branches, usually two larger and one smaller ; they 

 course in the M. otjliq. aJjdom. intern us (Fig. I22 oi) to the M. rectus, 

 where they give off branches, then pierce the muscle to reach the 

 skin {R. cutaneus atxlominalis), (Fig. 122 IIIc). 



4. The fourth spinal nerve (i\^. spinalis IV) (Fig. 126 31 4) 

 appears between the fourth and fifth vertebrae ; it runs on the 

 ventral surface of the transverse process of the fifth vertebra and 

 upon the Muse, intertransversariiis obliquely outwards and down- 

 wards, and reaches the deeper surface of the Muse, ohliquus internus, 

 into which it descends, about opposite the articulation between the 

 eighth and ninth vertebrae ; it then bifurcates into : — 



(i) A Ramus cutaneus ahdominalis, which pierces the muscle and 

 supplies the skin. 



(2) A Ramus muscularis,, which supplies the broad abdominal 

 muscle and the M. rectus ahdominis. 



5. The fifth spinal nerve {N. spànalis V) (Fig. 126 il/5) emerges 

 through the foramen between the fifth and sixth vertebrae, runs 



