490 



THE SPINAL CORD. 



Fk. 343. 



its lower part, where they are 

 closely crowded together, the roots 

 of the lumbar and sacral nerves 

 descend nearly vertically to reach 

 the lumbar intervertebral and the 

 sacral foramina, and form a large 

 bundle of nervous cords named the 

 cmidn cgy.ina, which occupies the 

 vertebral canal below the termina- 

 tion of the cord (17, fig. 345). 



Fig. 343. — View of the Cerebro- 

 spinal Axis op the Nervous System: 

 (after Bourgery). i 



The right half of the cranium and 

 trunk of the body has been removed by 

 a vertical section ; the membranes only of 

 the brain and spinal marrow have been 

 removed, and the roots and first part of 

 the fifth and ninth cranial, and of all 

 the spinal nerves of the right side, have 

 been dissected out and laid separately on 

 the wall of the skull and on the several 

 vertebras opposite to the place of their 

 natui-al exit from the cranio-spinal cavity. 



F, T, 0, lateral surface of the 

 cerebrum ; C. cerebellum ; P, pons 

 Varolii ; m o, medulla oblongata ; m s, 

 upper and lower extremities of the spinal 

 marrow ; c e, on the last lumbar ver- 

 tebral spine, marks the cauda equina ; v, 

 the three principal branches of the nervous 

 trigeminus or fifth pair ; G i, the sub- 

 occipital or first cervical nerve ; above 

 this is the ninth jjair ; G viii, the eighth 

 or lowest cervical nerve ; D i, the first 

 dorsal nerve ; D xii, the last or twelfth ; 

 L I, the first lumbar nerve ; L v, the last 

 or fifth ; S i, the first sacral nerve ; S v, 

 the fifth ; Co i, the coccygeal nerve ; s, 

 the left sacral plexus. 



Although the cord usually ends 

 near the lower border of the body of 

 the first lumbar vertebra, it sometimes 

 terminates a little above or below 

 that point, as opposite to the last 

 dorsal or to the second lumbar verte- 

 bra. The position of the lower end of 

 the cord also varies according- to the 

 state of curvature of the vertebral 

 column, in the flexion forn'ards of 

 which, the end of the cord is slightly 

 raised. In the foetus, at an early 

 period, the cord occuj^ies the w^hole 

 length of the vertebral canal ; but, 

 after the third month, the canal and 

 the roots of the lumbar and sacral 

 nerves begin to grow more rapidly 

 than the cord itself, so that at birth 

 the lower end reaches only to the 

 third lumbar vertebra. 



