162 



THE HUMAN BODY. 



70), which runs back to the end of the neural canal behind 

 the sacrum. In its course the cord presents two expansions, 

 an upper, 10, the cervical enlargement, reaching from the third 

 cervical to the first dorsal vertebrae, and a lower or lumbar 

 enlargement, 9, opposite the last dorsal vertebra. 



Running along the middle line on both the ventral and the 

 dorsal aspects of the cord is a groove, and a cross-section shows 

 that these grooves are the surface indications of fissures which 

 extend deeply into the cord (C, Fig. 71) and nearly divide it 

 into right and left halves. 



The anterior fissure (1, Fig. 71) is wider and shallower 

 than the posterior, 2, which indeed is hardly a true fissure, 

 being completely filled up by an ingrowth of pia mater. The 

 transverse section, C, shows also that the substance of the 



FIG. 71. The spinal cord and nerve-roots. A, a small portion of the cord seen 

 from the ventral side; B, the same seen laterally ;<?, a cross section of the cord; 

 D, the two roots of a spinal nerve; 1. anterior (ventral) fissure; -', posterior (dorsal) 

 fissure; 3, surface groove along the line of attachment of The anterior nerve-roots; 

 4, line of origin of the posterior roots; 5, anterior root filaments of spinal perve; 

 6. posterior root filaments; 0', ganglion of the posterior root; 7, 7', the first two 

 divisions of the nerve-trunk after its formation by the union of the two roots. The 

 grooves are much exaggerated. 



cord is not alike throughout, but that its white superficial 

 layers envelop a central gray substance arranged somewhat in 

 the form of a capital H. Each half of the gray matter is 

 crescent-shaped, and the crescents are turned back to back and 

 united across the middle line by the gray commissure. The 



