THE SPINAL CORD 



77 



rather than in the accurate linear order characteristic of the dorsal roots. Those 

 from a given segment unite with each other to form a ventral root; and that in 

 turn joins with the corresponding dorsal root just beyond the spinal ganglion to 

 form the mixed nerve (Fig. 50). 



Relation of the Spinal Cord and Nerve Roots to the Vertebral Column. 

 At an early fetal stage the spinal cord occupies the entire length of the vertebral 



Infrahyoid muscles 



Diaphragm 



Muscles of shoulder, arm, 

 and hand 



Cervical segments of spinal cord 



Thoracic segments of spinal cord 



Lumbar segments of spinal cord 



Sacral and coccygeal segments of 

 spinal cord 



Abdominal musdes 



Flexors of hip / 



Extensors of the kneel 



and adductors of hip[ 



Other muscles of thigh, 

 leg, and foot 



Perinea! and anal mus- 

 cles 



Fig. 53. Diagram showing the level of the various segments of the spinal cord with reference to 

 the vertebra?, with a table showing the distribution of the fibers of the several ventral roots. 



canal and the spinal nerves pass horizontally lateralward to their exit through 

 the intervertebral foramina. As development progresses the vertebral column 

 increases in length more rapidly than the spinal cord, which, being firmly an- 

 chored above by its attachment to the brain, is drawn upward along the canal, 

 until in the adult it ends at about the lower border of the first lumbar vertebra. 



