ANATOMY OF THE NERVOUS SYSTEM 



143 



opposite the outer margin of the foramen magnum of the occipital 

 bone: from there it extends to the articulation between the first and 

 second lumbar vertebrae, where it narrows off to a slender non- 

 nervous filament, the filum terminate (cut off and represented 

 separately at B f in Fig. 56), 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 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. 57.-^-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; 

 (>', 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. 57) and nearly divide it into 

 right and left halves. 



The ventral fissure (1, Fig. 57) 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, 



