THE SPINAL NERVES 



123 



The posterior nerve-roots are purely sensory, and they enter 

 the spinal medulla at the apex of the posterior column 

 of grey matter. Each posterior nerve-root has a ganglion 

 upon it containing cells, which send peripheral fibres into 

 the nerve and central fibres into the spinal medulla, where 

 they establish connexions with the higher neurones. The 

 two nerve-roots unite with one another in the intervertebral 

 foramen to form a spinal nerve, which divides, almost at once, 

 into anterior and posterior rami (primary divisions) (Fig. 59). 



FIG. 59. Diagram to illustrate the course taken by Sensory Fibres 

 after entering the Spinal Medulla. 



A. Spino-thalamic tract (painful, thermal 



and tactile sensations). 



B. Posterior funiculus of spinal medulla 



(muscle and joint sense, and a few 

 tactile fibres). 



C. Anterior nerve-root. 



D. Posterior nerve-root 



E. Anterior ramus (primary division). 



F. Posterior ramus. 



K. Typical spinal nerve. 



As the spinal medulla is much shorter than the vertebral 

 canal, in which it lies, the nerve-roots in the cervical region 

 are much shorter than those in the thoracic and other regions, 

 and the lower part of the canal is occupied by the long nerve- 

 roots of the lower lumbar, the sacral and the coccygeal 

 nerves. 



Both of the rami into which each spinal nerve divides are 

 mixed nerves. The posterior rami (primary divisions) are 

 entirely distributed to the muscles and skin of the back of the 

 trunk, neck and head. The anterior rami form the cervical, 



