124 THE NERVOUS SYSTEM 



brachial, lumbar, sacral and pudendal plexuses, while, in the 

 thoracic region, they constitute the intercostal nerves. 



The spinal nerves are named according to the region of the 

 vertebral column at which they emerge from the vertebral 

 canal. Thus there are eight cervical, twelve thoracic, five lumbar, 

 five sacral and one coccygeal nerve on each side of the body. 



THE POSTERIOR RAMI (PRIMARY DIVISIONS) 



Each posterior ramus, typically, divides into lateral and 

 medial branches, of which one is distributed to both skin and 

 muscles, while the other supplies muscles only. 



The First Cervical Nerve sends no branches to the skin, 

 but the medial branch of the second, termed the greater 

 occipital nerve, ascends over the back of the scalp and supplies 

 an extensive cutaneous area. It is usually aided in this dis- 

 tribution by the third occipital nerve, which represents the 

 medial branch of the third cervical nerve. In the occipito- 

 cervical type of neuralgia, the pain is experienced over the 

 area supplied by the two occipital nerves. 



The fourth, fifth and sixth cervical nerves supply the skin 

 of the back of the neck above the level of the superior border 

 of the scapula, but the seventh and eighth cervical nerves 

 are distributed solely to muscles (Fig. 60). 



The upper thoracic nerves supply the extensor muscles of 

 the vertebral column, and their cutaneous branches supply 

 horizontal bands of skin extending from the median plane to 

 the posterior axillary line (Fig. 60). The lower thoracic 

 nerves give off corresponding motor branches and their 

 cutaneous branches become increasingly oblique, so that the 

 twelfth supplies the skin over the iliac crest. 



In the upper three lumbar nerves, which have a similar 

 distribution, this obliquity becomes still more marked, and 

 their terminal branches supply the skin of the buttock. The 

 fourth and fifth lumbar nerves do not reach the skin. 



The upper three sacral nerves give off branches to the 



