SPINAL CORD. 



575 



Fig. 322. Spinal Cord. 

 Side View. Plan of the Fis- 

 sures and Columns. 



the anterior median fissure; and, on its posterior surface, another fissure, which 

 also extends along the entire length of the cord, the posterior median fissure. 

 These fissures serve to divide the cord into two symmetrical halves, which are 

 united in the middle line, throughout their entire length, by a transverse band 

 of nervous substance, the commissure. 



The anterior median fissure is wider, but of less depth than the posterior, 

 extending into the cord for about one-third of its thickness, and is deepest at 

 the lower part of the cord. It contains a prolongation from the pia mater; and 

 its floor is formed by the anterior white commissure, which is perforated by 

 numerous bloodvessels, passing to the centre of the cord. 



The jwsterior median fissure is much more delicate than the anterior, and most 

 distinct at the upper and lower parts of the cord. It extends into the cord to 

 about one-half of its depth. It contains a very slen- 

 der process of the pia rnater, and numerous blood- 

 vessels, and its floor is formed by a thin layer of 

 white substance, the posterior white commissure. 

 Some anatomists state, that the bottom of this fissure 

 corresponds to the gray matter, except in the cervical 

 region, and at a point corresponding to the enlarge- 

 ment in the lumbar region. 



Lateral Fissures. On either side of the anterior 

 median fissure, a linear series of foramina may be 

 observed, indicating the points where the anterior 

 roots of the spinal nerves emerge from the cord. 

 This is called, by some anatomists, the anterior 

 lateral fissure of the cord, although no actual fissure 

 exists in this situation. And on either side of the 

 posterior median fissure, along the line of attachment 



of the posterior roots of the nerves, a delicate fissure may be seen, leading 

 down to the gray matter which approaches the surface in this situation: this is 

 called the posterior lateral fissure of the spinal cord. On the posterior surface 

 of the spinal cord, on either side of the posterior median fissure, is a slight 

 longitudinal furrow, marking off two slender tracts, the posterior median 

 columns. These are most distinct in the cervical region, but are stated by 

 Foville to exist throughout the whole length of the cord. 



Columns of the Cord. The fissures divide each half of the spinal cord into 

 four columns, an anterior column, a lateral column, a posterior column, and a 

 posterior median column. 



The anterior column includes all the portion of the cord between the anterior 

 median fissure and the anterior lateral fissure, from which the anterior roots 

 of the nerves arise. It is continuous with the anterior pyramid of the medulla 

 oblongata. 



The lateral column, the largest segment of the cord, includes all the portion 

 between the anterior and posterior lateral fissures. It is continuous with the 

 lateral column of the medulla. By some anatomists, the anterior and lateral 

 columns are included together, under the name of the antero-lateral column, 

 which forms rather more than two-thirds of the entire circumference of the cord. 



The posterior column is situated between the posterior median and posterior 

 lateral fissures. It is continuous with the restiforrn body of the medulla. 



The posterior median column is that narrow segment of the cord which is seen 

 on each side of the posterior median fissure, usually included with the pre- 

 ceding, as the posterior column. 



Structure of the Cord. If a transverse section of the spinal cord be made, it 

 will be seen to consist of white and gray nervous substance. The white matter 

 is situated externally, and constitutes the greater part. The gray substance 

 occupies the centre, and is so arranged as to present on the surface of the sec- 

 tion two crescentic masses placed one in each lateral half of the cord, united 



