THE REGIONS OF THE SPINAL CORD 



483 



FIG. 378. TRANSECTION OF THE SPINAL COBD OF 

 A CHILD, FIFTH LUMBAR SEGMENT. 



Weigert stain, x 7. 



These nerve trunks also supply to the cord a great number of 

 centripetal or sensory fibres which enter the dorsal and, later 

 (through secondary neu- 

 rones), the lateral col- 

 umns; thus both of these 

 columns are of large size 

 in and above the lumbar 

 region. The postero-in- 

 ternal column in this re- 

 gion attains an appreci- 

 able size, and a distinct 

 pial septum marks its 

 lateral boundary. 



The spinal cord is now 

 nearly circular in tran- 

 section, its ventrodorsal 

 being perhaps slightly 

 greater than its transverse diameter. The grey commissure lies 

 very near the middle of the spinal cord, and the anterior median 

 fissure is, therefore, quite as deep as the posterior median septum. 



Both the ventral and dorsal grey horns are long and thick. 

 Each dorsal horn contains a large area of gelatinous substance, is 

 somewhat longer on its lateral than on its median side, and reaches 

 nearly to the dorsal surface of the spinal cord, opposite the postero- 

 lateral sulcus. The dorsal nerve roots entering at this level are 

 apparently directed toward the middle of the tips of the dorsal 

 horns of grey matter ; once within the spinal cord they pass around 

 to the median side of the dorsal horns. 



The ventral horns, somewhat larger than the dorsal, present 

 two short and broad protuberances, the one at the antero-mesial, 

 and the other and more prominent at the antero-lateral angle. A 

 similar though less prominent protuberance is seen at the base of 

 the ventral horn, on its lateral aspect. Each of these projections 

 contains a more or less well-defined group of motor nerve cells. 

 The cell groups of the anterior horns in the lumbar region are 

 therefore a ventro-medial, ventro-lateral, and dor so-lateral, together 

 with an ill-defined central group occupying the deeper " interme- 

 diate zone " of grey matter. 



The nerve centers contained in the lumbar region control the 

 reflexes and musculature of the lower limbs and the lower part of 

 the abdominal wall. 



