122 



THE HUMAN BODY 



ment, the filum terminals (cut off and represented separately at 

 B' in Fig. 58), which runs back to the end of the neural canal 

 behind the sacrum. In its course the cord presents two expan- 

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

 third cervical to the first dorsal vertebra, 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 



.6' 



FIG. 59. The spinal cord and nerve-roots. A, a small portion of the cord seen 

 from the ventral side; B, the same seen laterally; C, a cross-section of the cord; 

 D, the two roots of a spinal nerve; 1, ventral fissure; 2, dorsal fissure; 3, surface 

 groove along the line of attachment of the ventral nerve-roots; 4, line of origin of 

 the dorsal roots ; 5, ventral root filaments of spinal nerve ; 6, dorsal root filaments ; 

 6', ganglion of the dorsal 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. 



that these grooves are the surface indications of fissures which 

 extend deeply into the cord (C, Fig. 59) and nearly divide it into 

 right and left halves. 



The ventral fissure (I, Fig. 59) is wider and shallower than the 

 dorsal, 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 cord is not alike through- 

 out, but that its white superficial layers envelop a central gray 

 substance arranged somewhat in the form of a capital H. Each 



