CHAP. X.] 



THE SPINAL CORD. 



257 



the sides and front of that half of the cord, limited in front by the 

 anterior fissure, and posteriorly by the posterior horn. The pos- 

 terior column is situated behind the posterior horn of gray matter, 

 and is separated from its felloAV of the opposite side by the posterior 

 fissure. The antero-lateral columns are united across the middle 

 line by the anterior or white commissure ; the gray crescents, by the 

 posterior or gray commissure ; while the pos- ~ 66 



terior columns are not connected, except where 

 the posterior fissure is imperfect or deficient. 



In the different regions of the cord great va- 

 riety exists as regards the quantity of gray and 

 white matter, and the disposition of the lateral 

 portions of the former. There seems to be a 

 much greater proportion of gray matter to white 

 in the lumbar, than in the cervical or dorsal 

 region of the cord. In the cervical region the 

 crescentic portions are small, and the white mat- 

 ter is abundant. That portion of the white sub- 

 stance which is placed between the posterior gray 

 horns, is augmented by the existence of two 

 small columns (posterior pyramids) , which ex- 

 tend from the medulla oblongata into this re- 

 gion. In the dorsal region the gray matter is at 

 its minimum of development, and the white 

 matter is likewise small in quantity. The dimi- 

 nution in the quantity of the latter appears more 

 striking as effects the antero-lateral, than the 

 posterior columns. In the lumbar region both 

 the horns of the gray matter are manifestly 

 thicker, and the stellate character of the anterior 

 horn is well marked. Towards the inferior ex- 

 tremity of the cord the white matter appears 

 gradually to cease, leaving the gray to form the Transverse sections the 



principal constituent, until, in the commence- *&?*} ccr(i = A - immediate- 

 ly below the decussation of 



rnentofthefiliformprocess.it is found alone the pyramids. B. At middle 



of cervical bulb. c. Midway 



(llff . 66 ). between cervical and lumbar 



yL bulbs. D. Lumbar bulb. E. 



Ine roots of the spinal nerves emerge from An inch lower, p. very near 



.^ the lower end. a. Anterior 



the cord on each side along; two lines which are surface - P. Posterior surface. 



The points of emergence of 



separated bv the ligamentum dentatum. The the anterior and posterior 



. roots of the nerves are also 



posterior line corresponds to the margin of the seen - 

 posterior horn of gray matter, the anterior one is placed about 

 midway between it and the anterior fissure. When the roots of 

 VOL.I. s 



E 



