688 



THE NEEVOUS SYSTEM. 



and laterally among the muscles, and become superficial at a greater distance from 

 the median plane. In both regions the nerves pursue a sinuous course to the 

 surface, and the lower series emerge and 

 become superficial a considerable distance 

 below the level of their spinal origin. 

 There are considerable individual differ- 

 ences in the origin, course, and distribu- 

 tion of the several nerves. 



CERVICAL NERVES. 



First Cervical Nerve (N. sub-occip- 

 italis). It has already been pointed out 

 that the posterior root of this nerve may 

 be very small, 

 or even absent 

 altogether. Its 

 posterior ramus 



is larger than 

 the anterior 

 ramus ; it does 

 not divide into 

 medial or lat- 

 eral branches, 

 and it does not 

 directly supply 

 any cutaneous 

 branch. 



Passing 

 backwards, in 

 the space be- 

 tween the oc- 

 cipital bone and 

 the posterior 

 arch of the atlas, 

 the nerve occu- 

 pies the sub-oc- 

 cipital triangle, 

 and is placed 

 below and be- 

 hind the ver- 

 tebral artery, 

 and under cover 

 of the semi- 

 spinalis capitis 

 muscle. It sup- 

 plies the follow- 

 ing branches: 



(a) Muscular 

 branches to the 

 semispinalis 



FIG. 607. THE DISTRIBUTION OP CUTANEOUS NERVES ON THE BACK OF THE TRUNK. 

 On one side the distribution of the several nerves is represented, the letters indicating their nomenclature. 



G.O (C.2), Greater occipital ; C.3, Third occipital ; T.I et seq., Posterior rami of thoracic nerves ; L.I et seq., 

 Posterior rami of first three lumbar nerves ; S.I et seq., Posterior rami of sacral nerves ; Acr, Posterior 

 supra-clavicular branches from cervical plexus ; T.2-12, Lateral branches of thoracic nerves ; Circ. 

 Cutaneous branches of axillary nerve ; L.I, Iliac or lateral cutaneous branch of ilio-hypogastric nerve 

 E.C, Lateral cutaneous nerve of thigh ; S.Sc, Posterior cutaneous nerve of thigh. 



On the other side a schematic representation is given of the areas supplied by the above nerves, the numeral 

 indicating the spinal origin of the branches of distribution to each area. 



