410 



CERVICAL NERVES. 



Fig. 185.* 



sulcus, on the antero-lateral column of the spinal cord, and gradually ap- 

 proach towards the anterior longitudinal fissure as they descend. 



The posterior roots, more regular than the 

 anterior, proceed from the posterior lateral 

 sulcus, a narrow grey stria, formed by the in- 

 ternal grey substance of the cord. They are 

 larger, and the filaments of origin more nu- 

 merous than those of the anterior roots. In 

 the intervertebral foramina there is a ganglion 

 on each of the posterior roots. The first cer- 

 vical nerve forms an exception to these cha- 

 racters ; its posterior root is smaller than the 

 anterior ; it often joins in whole or in part 

 with the spinal accessory nerve and some- 

 times with the hypoglossal : there is frequently 

 no ganglion upon it, and when the ganglion 

 exists it is often situated within the dura 

 rnater, the latter being the usual position of the ganglia of the last two pairs 

 of spinal nerves. 



After the formation of a ganglion, the two roots unite and constitute a 

 spinal nerve, which escapes through the intervertebral foramen and divides 

 into an anterior branch for the supply of the front aspect of the body, and 

 a posterior branch for the posterior aspect. In the first cervical and two 

 last sacral nerves this division takes place within the dura mater and in 

 the upper four sacral nerves externally to that cavity, but within the sacral 

 canal. The anterior branches, with the exception of the first two cervical 

 nerves, are larger than the posterior ; an arrangement which is propor- 

 tioned to the larger extent of surface they are required to supply. 

 The Spinal nerves are divided into 



Cervical 

 Dorsal 

 Lumbar 

 Sacral 



8 pairs. 

 12 

 5 

 6 



The cervical nerves pass off transversely from the spinal cord ; the dor- 

 sal are oblique in their direction ; and the lumbar and sacral vertical ; the 

 latter form the large assemblage of nerves at the termination of the cord 

 called cauda equina. 



CERVICAL NERVES. 



The cervical nerves increase in size from above downw r ards ; the first 

 (sub-occipital) passes out of the spinal canal between the occipital bone 

 and the atlas ; and the last, between the last cervical and first dorsal ver- 



* Part of the cervical portion of the spinal cord, viewed on its posterior aspect ; and 

 Knowing its membranes and the posterior roots of the spinal nerves. 1, 1. The fissura 

 longitudinalis posterior. 2, 2. The posterior roots of the cervical nerves ; on the oppo- 

 Bite side the corresponding roots are cut through near their origin. 3, 3. The membrana 

 dentata. 4. The nervus accessorius, ascending between the posterior roots and the 

 membrana dentata; on the opposite side this nerve has been removed. 5, 5. The dura 

 mater or thrca vertebralis. 6, 6. Openings in the dura mater for the passage of tho 

 roots of the nerves. 7, 7. The ganglia on the posterior roots of the spinal nerves. 8. 

 The anterior roots of the spinal nerves. The posterior roots have been cut a\v;iy iu 

 rder to show each anterior root, proceeding to join the nerve beyond the ganglion. 



