390 PI A MATER. 



nervous matter of the cord protrudes. Its external surface 

 is rather rough from the cellular and fibrous filaments con- 

 necting it with the arachnoid. On this surface are also seen 

 large and tortuous vessels." Its internal surface is connected 

 by delicate vessels and cellular threads to the cord. The 

 pia mater, besides surrounding the spinal marrow, sends 

 a duplication into both its anterior and posterior median 

 fissure, and also gives a neurilemma to each nerve. 



The function of this membrane is rather one of protection 

 to the spinal cord, than that of a vascular membrane as 

 upon the brain. 



The Spinal Marrow, (Fig. 14,) it has been stated under 

 the head of the nervous tissue, consists of two kinds of 

 nervous matter, the white and the gray, not disposed as 

 they are in the brain. The white or medullary forms 

 the whole exterior covering, while the gray or cineritious 

 occupies the interior. 



Besides its division into two lateral and symmetrical 

 parts by the anterior and posterior median fissures, and 

 the lateral subdivision of these, by two other fissures, 

 so that each half of the cord consists of three columns 

 or rods, according to Sir Charles Bell, the anterior and 

 posterior columns, and the middle or respiratory tract; 

 two others have been added by some, making the cord 

 consist of eight divisions, four on each side of the median 

 fissure, in the following manner : first, the anterior, between 

 the median fissure and anterior nerves; second, the lateral 

 between the roots of the nerves; third, the posterior between 

 the posterior fissure and posterior nerves; and fourth, the 

 posterior pyramids, situated only at the upper part of the 

 cord, and close to the posterior fissure. 



Another division of the spinal marrow, and one thought 

 most natural, is the blending together of the anterior and 

 middle columns, under the head of antero lateral, and count- 

 ing the posterior column as one, making but four in all. 

 The bottoms of the anterior and posterior fissures, have 

 transverse bands or commissures, extending from side to 

 side,, and connecting the lateral halves of the spinal cord. 



