354 THE SPINAL CORD. 



TRACTS OF THE SPINAL CORD. 



The antero-lateral fasciculus proprius (fasciculus antero- 

 lateralis proprius) occupies the deep part of the anterior and lateral 

 columns (Figs. 102 and 103). It embraces the anterior columna 

 of gray matter and covers the outer surface of the center of the 

 crescent and the base of the posterior columna. By the most 

 lateral anterior root-fibers it is subdivided into anterior and lateral 

 fasciculi. It approaches, but does not quite reach, the surface 

 of the cord. Notice that it is separated from the anterior median 

 fissure by the anterior pyramidal tract, and that the anterior cere- 

 bello-spinal and spino-thalamic tracts run between it and the 

 surface of the cord. Behind, it is in relation with the lateral pyram- 

 idal tract. The antero-lateral fasciculus proprius is composed 

 of ascending and descending fibers which are the T-branches 

 of axones from the gray crescent. It is largely a short fiber tract, 

 associative and commissural in function. That part situated in 

 the anterior column, the anterior fasciculus proprius, is largely 

 commissural, between the anterior columna:; while the lateral 

 fasciculus proprius is chiefly associative, and connects different 

 segments of the cord on the same side. The antero-lateral fas- 

 ciculus proprius is continued in the substantia reticularis of the 

 medulla, and the reticular formation of pons and mid-brain, 

 constituting a short fiber tract which extends from the lower part 

 of the cord to the basal ganglia of the cerebrum. In the anterior 

 fasciculus proprius there is a strand of long fibers called the me- 

 dial longitudinal bundle (fasciculus longitudinalis medialis). . 



The medial (posterior] longitudinal bundle is composed of an 

 ascending and a descending strand of fibers (Figs. 102 and 103). 

 The ascending strand rises from the anterior columna in each 

 segment of the spinal cord and runs upward to the motor nuclei 

 of cerebral nerves and terminates in them. Perhaps a few fibers 

 reach the thalamus. It ascends just ventro-medial to the anterior 

 columna in the cord; in the medulla, it runs between the head 

 of the anterior columna and the pyramidal decussation, then just 

 lateral to the fillet decussation, after which, it takes its dorso-medial 

 position along the raphe. Its junction is reflex. The descending 



