POSTERIOR CERVICAL NERVES. 365 



The complexus is concealed by the splenis and trapezius : and the cuta- 

 neous surface is marked by a tendinous cross intersection towards the 

 upper end. Two or three of the cervical nerves perforate it. Along the 

 inner side is the semispinalis muscle, with the ligamentum nuclue. Be- 

 neath it are the small recti and obliqui muscles, the semispinalis, and the 

 cervical nerves and vessels. 



Action. Both muscles will move the head directly back. One will 

 draw the occiput down and back towards its own side. 



Dissection of vessels and nerves (fig. 119). In the neck the nerves and 

 vessels will be brought into view by detaching the complexus from the 

 occipital bone and the spine of the seventh vertebra, and throwing it out- 

 wards carefully from the subjacent parts. Beneath the muscle is a dense 

 fascia, in which are contained the ramifications of the cervical nerves, and 

 the deep cervical and other vessels. 



Each nerve except the first divides into an inner and an outer piece. 

 Dissect out first the inner pieces of the seven lowest, which lie partly over 

 and partly beneath the fibres of the semispinalis muscle (G). The exter- 

 nal pieces ( 3 ) are very small ; they are given off between the transverse 

 processes close to where the trunks appear ; they are to be looked for outside 

 the complexus, and enter the muscles prolonged from the erector spinae. 



The first or suboccipital is the most difficult of the set to find : this little 

 nerve is a short trunk, which is contained in the interval between the 

 small recti and obliqui muscles near the head ; it will be best found by 

 looking for the small twigs furnished by it to the muscles around. 



The deep cervical artery is met with on the semispinalis muscle ; a part 

 of the vertebral artery will be found in contact with the suboccipital 

 nerve ; and the occipital artery will be seen crossing the occipital bone. 



* Opposite the thorax the dorsal nerves and vessels will be readily dis- 

 played on the inner side of the longissimus dorsi muscle, on the removal 

 of a little fatty tissue from between the transverse processes. External 

 and internal pieces are to be traced from each nerve and vessel into the 

 muscles ; some of the former have been seen in the interval between the 

 ilio-costalis and the longissimus dorsi. 



* The two pieces of the lumbar nerves and vessels will be found in the 

 same line as the dorsal ; but the inner set are the most difficult to be dis- 

 covered. 



* The small sacral nerves are placed beneath the multifidus spince, and 

 will be dissected after the examination of that muscle (p. 372). 



* POSTERIOR PRIMARY BRANCHES OF THE SPINAL NERVES. The 

 spinal nerves, with a few exceptions in the cervical and sacral groups, 

 bifurcate in the inter vertebral foramina into anterior and posterior primary 

 branches (p. 165). The posterior supply the integuments and the muscles 

 of the back, and are now to be learnt. 



In the neck. The posterior primary branches of the cervical nerves are 

 eight in number, and issue between the transverse processes ; but those of 

 the first and second, which begin on the neural arches of the atlas and 

 axis, cross those arches. All, except the first, divide into internal and 

 external pieces. 



The external pieces (fig. 118) are very inconsiderable in size, and end 

 in the splenius, and in the muscles prolonged from the erector spinw. 



The intern al pieces (fig. 119) are larger than the external; they are 

 directed towards the spinous processes, the three lowest nerves passing 

 beneath the semispinalis, and the four next over that muscle. By the side 



