GRAY MATTER OF THE CORD. 343 



anterior commissure into the anterior nerve-roots of the oppo- 

 site side, and others enter into the fasciculi proprii of the cord. 

 The lateral column of cells in the anterior columna is a large 

 one (Figs. 102 and 103). It is found only in the regions which 

 innervate the extremities, that is, in the cervical and lumbar 

 enlargements. It is everywhere divided into a ventro-lateral and a 

 dorso-lateral cell-group, and in most of the segments of the lumbar 

 enlargement there are two other cell-groups, according to Alexander 

 Bruce. One of them is located behind the dorso-lateral cells 

 and is called the post-dor so-lateral group; and the other, which 

 occupies the angle between the ventro-lateral and the dorso-lateral 

 cells, lying medial to both, is called the central group (Cunning- 

 ham). The dendrites of the cell-bodies in the lateral column 

 arborize and end both in the gray matter of the anterior columna 

 and in the white matter adjacent to its lateral surface; the axones 

 proceed largely into the anterior roots of the spinal nerves but partly 

 into the longitudinal white columns of the cord. Probably the 

 medial column innervates the trunk muscles; the lateral column, 

 the muscles of the extremities. Cortical Connection. These 

 cell-columns are brought into relation with the anterior (direct) 

 pyramidal fibers and the lateral (crossed) pyramidal fibers by 

 means of intermediate neurones. In this manner motor and 

 inhibitory impulses descend to them from the cerebral cortex, 

 coming from the opposite hemisphere, chiefly, but also from the 

 same side. They also are in relation with the end-tufts of posterior 

 root-fibers and with axones whose cell-bodies are located in the 

 center and posterior columna of the gray crescent. The latter 

 neurones form contact relations with fibers of the posterior roots 

 of the spinal nerves on both sides. Thus both by immediate 

 contact between anterior and posterior root-neurones and by the 

 intervention of an intrinsic spinal neurone the simple reflex mechan- 

 ism of the spinal cord is formed. It has been the belief that the 

 end-tufts of the fibers in the anterior and lateral pyramidal tracts 

 are in. direct contact with the dendrites or cell-bodies of the neu- 

 rones in the anterior columna; but the investigations of Schafer, 

 Collier and others, indicate that this connection between the 

 neurones of the anterior columna and the lateral pyramidal fibers, 



