696 



THE NERVOUS SYSTEM. 



of the cord, so that in the child at birth the cord extends as far as the third lum- 

 bar vertebra. Its position varies also according to the degree of curvature of the 



Pyramid 



Decussation 



of the 

 pyramids 



Ant. med. 

 fissure 



Antero-lat.. 



Posterior 

 Median Fissure. 



Intumescentia 

 lumbalis, or 

 lumbar en- 

 largement 



Conus 

 terminalis 



Beginning of 

 thefllum term. 



FIG. 402. The spinal cord : A, from in front. B, from 

 behind. (Gegenbaur and Ouain.) 



FIG. 403. Spinal cord. Side 

 view. Plan of the fissures and 

 columns. 



spinal column, being raised somewhat 

 in flexion of the spine. On exam- 

 ining its surface it presents a differ- 

 ence in its diameter in different parts, 

 being marked by two enlargements, 

 an upper or cervical, and a lower or 

 lumbar. The cervical enlargement, 

 which is the larger, extends from 

 about the third cervical to the first 

 or second dorsal vertebra : its great- 

 est diameter is in the transverse di- 

 rection, and it corresponds with the 

 origin of the nerves which supply the 

 upper extremities. The lower, or lum- 

 bar, enlargement (intumescentia) is 

 situated opposite the last two or three 

 dorsal vertebrae, its greatest diameter 

 being from before backward. It cor- 

 responds with the origin of the nerves 

 which supply the lower extremities. 

 In form the spinal cord is a flattened 

 cylinder (Fig. 402). 



Fissures. It presents on its ante- 

 rior surface, along the middle line, a 

 longitudinal fissure, the anterior me- 

 dian fissure, and on its posterior sur- 

 face another fissure, which also ex- 

 tends along the entire length of the 

 cord, the posterior median fissure. 

 These fissures penetrate through the 

 greater part of the thickness of the 

 cord, and incompletely divide the 

 cord into two symmetrical halves, 

 united in the middle line by a trans- 

 verse 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 con- 



