374 C. JUDSON HERRICK 



fibers enter the ventral tract b, chiefly between the levels of the 

 IX and X nerves, most of the bundles of arcuate fibers turning 

 cephalad within the tract, but some caudad. These tracts do not 

 extend beyond the limits of the area acustico-lateralis. At their 

 rostral ends they converge and the united tract reaches the tip 

 of the auricular lobe. Both of these tracts, particularly tract 

 a, are bordered laterally by a dense superficial neuropil in the 

 limiting zone of the white substance. From time to time fibers 

 leave the tracts to enter this outer plexiform layer and there 

 come into relation with dense dendritic arborizations of the neu- 

 rones of the area acustico-lateralis. It appears probable that 

 the fibers of these tracts are chiefly derived from the opposite side 

 of the oblongata, either as root fibers or secondary fibers. Each 

 neurone of the area acustico-lateralis would, in this case, engage 

 root fibers of its own side and also either root fibers or secondary 

 fibers from the area acustico-lateralis of the opposite side. 



There remain to be considered two important tracts concerned 

 with the correlation of sensory impressions from the spinal cord 

 to the oblongata, viz., the fasciculus dorso-lateralis of the spinal 

 cord and the tractus spino-bulbaris system. 



In the upper levels of the spinal cord there are bundles of fibers 

 dorsally and medially of the spinal V root (fig. 18, f.d.l.) which 

 appear to conduct impulses from the sensory area of the spinal 

 cord into the oblongata. This fasciculus dorso-lateralis of the 

 spinal cord can be followed forward into the vagus region as far 

 as the caudal end of the area acustico-lateralis, its rostral end 

 lying wholly ventrally of this area. Further details regarding 

 connections of these fibers have not been determined. They may 

 extend much farther forward. 



Ventrally of the fasciculus dorso-lateralis and spinal V root in 

 the caudal end of the oblongata is another ascending fasciculus 

 (fig. 17, tr.sp.t.), which in figures 12 to 17 is designated simply 

 tractus spino-tectalis. In reality this is a complex system of 

 fibers arising from unknown cells of the spinal cord and terminating 

 at intervals throughout the length of the oblongata, cerebellum, 

 midbrain and thalamus. Briefly, it is the spinal lemniscus and 

 spino-cerebellar system. 



