444 



THE SPINAL CORD. 



" multipolar" cells ; that is, they send out several prolongations in vari- 

 ous directions, transverse, longitudinal and oblique, most of which are 

 abundantly subdivided and terminate in minute ramifications, while a 

 single one frequently continues its course for a long distance undivided, 



Fig. 155. 



TRANSVERSE SECTION OF THE SPINAL CORD; lower cervical region. 1. Anterior 

 median fissure; immediately behind it are seen the decussating fibres of the white commis- 

 sure. 2. Central canal, situated in the middle of the gray commissure. 3. Posterior median 

 fissure. 4, 4. Anterior columns of white substance. 5, 5. Posterior columns. 6, 6. Lateral 

 columns. 7, 7. Anterior horns of gray substance. 8, 8. Posterior horns. 9, 9. Anterior 

 nerve roots. 10, 10. Posterior nerve roots. 



and assumes the appearance of an axis cylinder. They vary in form 

 and size in different parts of the gray substance. The most remarkable 

 of these cells are situated in the anterior horns, where they are dis- 

 tinguished by their large size, being, according to the measurements of 

 Kolliker, from 67 to 135 mmm. in diameter, the largest known cells in 

 the nervous system. They are arranged in two or three more or less 

 distinct groups near the extremity and outer portion of the anterior 

 horns. Beside these there are found scattered everywhere in the gray 

 substance, but more abundantly in the posterior horns, nerve cells which 

 are much smaller in size than the preceding, but of similar form and 

 provided with similar branching prolongations. The anterior and pos- 

 terior horns are not therefore absolutely distinguished from each other 

 by the character of their nerve cells, but only by the relative proportions 

 of their size and numbers ; since a few cells of comparatively large size 

 are found in the posterior horns, and the smaller ones exist in both 

 situations. 



