ANTERIOR DIVISIONS OF SPINAL NERVES. 575 



The posterior divisions of the last two sacral ne7'ves are smaller than 

 those above them, and are not divided into external and internal 

 branches. They are connected with each other by a loop on the back 

 of the sacrum, and the lowest is joined in a similar manner with the 

 coccygeal nerve ; one or two small filaments from these sacral nerves 

 are distributed behind the coccyx. 



Coccygeal Nerve. — The posterior division of the coccygeal nerve is 

 very small, and separates from the anterior primary portion of the 

 nerve in the sacral canal. It is joined by a communicating filament 

 from the last sacral nerve, and ends in the fibrous structure covering 

 the posterior surface of the coccyx. 



ANTERIOR PRIMARY DIVISIONS OF THE SPINAL 



NERVES. 



The anterior ])rimary divisions of the spinal nerves are distributed 

 to the parts of the body situated in front of the vertebral column, in- 

 cluding the limbs. They are, for the most part, considerably larger 

 than the posterior divisions. 



The anterior division of each spinal nerve is connected by one or 

 two slender filaments with the sympathetic. Those of the cervical, 

 lumbar, and sacral nerves form plexuses of various forms ; but those of 

 the dorsal nerves remain for the most part separate from one another. 



CERVICAL NERVES. 



The anterior divisions of the four upper cervical nerves form the 

 cervical plexus. They appear at the side of the neck between the 

 scalenus medius and rectus anticus major muscles. They are each 

 connected by a communicating filament with the first cervical ganglion 

 of the sympathetic nerve, or with the cord connecting that ganglion 

 with the second. 



The anterior divisions of the four lower cervical nerves, larger than 

 those of the upper four, appear between the scaleni muscles, and, 

 together with that of the first dorsal, go to form the brachial plexus. 

 They are each connected by a filament with one of the two lower cervical 

 ganglia of the sympathetic, or with the plexus on the vertebral artery. 



The anterior divisions of the first and second nerves require a notice 

 separately from the description of the nerves of the cervical plexus. 



SUB-OCCIPITAIi NERVE, 



The anterior primary division of the first nerve runs forwards in a 

 groove on the atlas, and bends downwards in front of the transverse 

 process of that vertebra to join tiie second nerve. In this course for- 

 wards it lies beneath the vertebral artery, and at the inner side of the 

 lectus lateralis muscle, to which it gives a branch. As it crosses the 

 ibramen in the transverse process of the atlas, the nerve is joined by a 

 filament from the sympathetic ; and from the loop which it makes in 

 front of the transverse process, branches are supplied to the two anterior 

 lecti muscles. Short filaments connect this part of the nerve with the 

 pneumo-gastric, the hypoglossal, and the sympathetic nerves. 



Valentin notices filaments distributed to the articulation of the occipital bone 

 with the atlas, and to the mastoid process of the temporal bone. 



