Cervical Plexus 143 



The inferior thyroid, coming off also from the thyroid axis, lies to the 

 inner side of the muscle till it turns inwards ; and the vertebral artery, 

 running up from the first part of the subclavian to the hole in the sixth 

 transverse process, is to the inner side of the scalenus anticus, which, 

 as already remarked, is inserted into the outer end of the transverse 

 processes. 



THE CERVICAL NERVES 



Though there are but seven cervical vertebrae, there are eight 

 cervical nerves, the first of which appears above the atlas, and the last 

 below the vertebra prominens. The anterior divisions of the first 

 four make up the cervical plexus, and those of the lower four join with 

 part of the first dorsal to form the brachial plexus. 



The posterior primary divisions of the cervical nerves divide, 

 ' for the most part, into an inner and an outer branch. But the 

 posterior division of the first, or sub-occipital nerve, does not divide ; 

 it emerges between the vertebral artery and the posterior arch of the 

 atlas, and supplies the obliqui, recti postici, and complexus. Some- 

 times it sends up a cutaneous branch to the back of the head, which 

 may be in great distress in the case of suboccipital disease. 



The posterior trunk of the second is much larger than the anterior. 

 Its internal division is the great occipital, which, as its name implies, 

 is a large branch for the back of the scalp. Passing through the in- 

 sertions of complexus and the trapezius, it accompanies the occipital 

 artery, and communicates with the lesser occipital nerve. The external 

 division is distributed solely to the erector spinas. 



The internal division of the third sometimes sends up an occipital 

 twig in addition to a branch for the skin of the nape of the neck. 

 The internal divisions of the fourth and fifth nerves give branches 

 to the erector spinse, as well as to the skin over the trapezius, whilst 

 those of the three lowest usually give off no cutaneous twigs. 



The external divisions of the posterior cervical nerves are for the 

 muscles only. 



The cervical plexus is formed by interlacements of the anterior 

 divisions of the first four cervical nerves. The anterior part of the 

 first) or sub-occipital nerve, is a slender branch, which winds forwards 

 from beneath the vertebral artery on the posterior arch of atlas, and at 

 the front of the first transverse process joins with a branch from the 

 second nerve. It ends in the supply of the recti laterales and antici. 



The anterior part of the second winds round the vertebral artery 

 in its course from beneath the posterior ring of the atlas, and gives a 

 division to the first nerve and one to the third. 



The anterior part of the third divides to join the second and the 

 fourth ; and the anterior part of the fourth, having received the last- 

 named branch, sends down a communicating twig to the fifth nerve, 

 which belongs to the brachial plexus. 



