292 



COORDINATION AND SENSATION 



SG. 



S<7. 



The Spinal Cord. This division of 

 the central nervous system is about 

 seventeen inches in length and two 

 thirds of an inch in diameter. It does 

 not extend the entire length of the 

 spinal cavity, as might be supposed, but 

 terminates at the lower margin of the 

 first lumbar vertebra. 1 It connects at 

 the upper end with the bulb, and termi- 

 nates at the lower extremity in a number 

 of large nerve roots, which are con- 

 tinuous with the nerves of the hips and 

 legs (Fig. 133). Two deep fissures, one 

 in front and the other at the back, ex- 

 tend, the entire length of the cord, and 

 separate it into two similar divisions. 

 These are connected, however, along 

 their entire length by a central band 

 consisting of both gray and white 

 matter. 



The arrangement of the neurons of 

 the spinal cord is just the reverse of 



*In very early life the spinal cord entirely fills the 

 spinal cavity, but as the body develops the cord grows 

 less rapidly than the spinal column, and, as a conse- 

 quence, separates at the lower end from the inclosing 

 bony column. 



FIG. 133. 



FIG. 133. Spinal cord, showing on one side 

 the nerves and ganglia with which it is closely 

 related in function. A. Bulb. B. Cervical enlarge- 

 ment. C. Lumbar enlargement. D. Termination 

 of cord. E. Nerve roots that occupy the spinal 

 cavity below the cord. P. Pons. D, G. Dorsal 

 root ganglia. S.G. Sympathetic ganglia. N. Nerve 

 trunks to upper and lower extremities. 



