600 



THE NERVOUS SYSTEM 



FIG. 519. TRANSECTION OF THE 

 SPINAL CORD OF A CHILD, 

 THIRD SACRAL SEGMENT. 



Weigert stain. X 7. 



nerve roots to which they give origin, we distinguish a sacral, lumbar, 

 thoracic, and cervical region. Each of these regions presents certain 



more or less important morphological 

 characteristics. 



In the sacral region the investment 

 of white matter is very thin, the gray 

 matter though actually less in amount 

 than in the more cephalad regions ap- 

 pearing large by comparison. Both the 

 ventral and dorsal horns of gray matter 

 are short and thick. The substantia 

 gelatinosa Eolandi is of considerable 

 volume. The cell groups in the ventral 

 horns of this region are a ventromedial 

 and a dorsolateral. 



The cord as a whole is small and its transection nearly circular in 

 outline. The five segments of this region contain the neuron centers 

 for the urinary bladder, the anus, some of the musculature of the lower 

 limbs, and the sensory reflexes 

 of the perineum and genito- 

 urinary organs. 



Below the sacral region the 

 spinal cord tapers rapidly 

 (conus medullaris) and is con- 

 tinued downward for a consid- 

 erable distance as the filum 

 terminale. The surrounding 

 leash of lumbar and sacral 

 nerve roots forms the cauda 

 equina. The fibrous mem- 

 branes which surround the 

 cord continue even farther 

 downward in the medullary 

 canal to form the central liga- 

 ment, which is finally attached to the sacrum or coccyx. 



In the lumbar region there is a distinct enlargement, chiefly in- 

 volving the gray substance, which here includes the immense number of 

 cells of the ventral horns whose 'motor' fibers enter the large lumbar 

 nerve trunks for the supply of the lower limbs. These nerve trunks 

 also supply to the cord a great number of centripetal or sensory fibers 



FIG. 520. TRANSECTION OF THE SPINAL 

 CORD OF A CHILD, FIFTH LUMBAR SEG- 

 MENT. 



Weigert stain. X 7. 



