CRANIAL CAVITY. 



noid space, which contains cerebrospinal fluid. The dura 

 mater, the most external, is dense and fibrous, and extends con- 

 siderably below the conus medullaris. The ligamenta denticu- 

 lata are two lateral, wing-like structures which support the cord 

 and extend from its sides to the inner surface of the dura where 

 they are attached by a series of pointed processes. [452] 



Fissures and Columns of the Cord. The antero-median fis- 

 sure runs the whole length in the midline anteriorly and pene- 

 trates slightly less than one-third of the diameter; the pia 

 dips into it. The postero-median fissure runs the whole length 

 in the midline posteriorly and penetrates half-way; it is very 

 narrow and receives no pia. These two fissures divide the cord 

 in halves; in the lumbar region they become of nearly equal 

 depth. Near the postero-median fissure, on each side, is a 

 shallow groove (postero-lateral sulcus) running the whole 

 length; the posterior nerve roots emerge at its bottom. It 

 divides each lateral half into a small posterior column and a 

 large antero-lateral column; the latter is arbitrarily divided, 

 by the line of anterior nerve roots, into a lateral column and 

 an anterior column. In the cervical region a distinct posterior 

 paramedian groove, nearer the postero-median than the postero- 

 lateral furrow, divides the posterior column into a column of 

 Burdock (funiculus cuneatus) externally, and a column of Goll 

 (Juniculus gracilis) internally; this groove is gradually lost in 

 the dorsal region. [454] 



Thirty-one pairs of spinal nerves arise from the spinal cord; 

 they are named according to their place of exit from the spinal 

 canal. In passing down in the canal, below the conus medul- 

 laris, to reach their places of exit they form a large bundle 

 (cauda equina) which encloses the filum terminale. [453] 



Internal Structure of Cord. The white matter is external 

 and the gray matter internal. On transverse section the gray 

 matter forms a crescentic mass, with the concavity outward, 

 in each lateral half; a transverse band (posterior gray com- 

 missure) connects the crescents and forms the bottom of the 



[51] 



