360 C. JUDSON HERRICK 



The descending dorsal and ventral VIII roots remain distinct 

 as far as the level of the second vagus root, beyond which they can 

 no longer be separated, the mixed root continuing to or beyond 

 the caudal end of the area acustico-lateralis. Below the level of 

 the fourth vagus root these fibers become mingled with those of 

 the fasciculus dorso-lateralis of the spinal cord and it has not 

 been possible to determine their caudal termination. Wallen- 

 berg ('07) in the frog traced descending VIII root fibers down- 

 ward as far as the sixth spinal segment. 



Some of the VIII root fibers at theii* entrance into the oblon- 

 gata are very coarse and some are fine. At their division within 

 the oblongata the coarse fibers divide into branches of unequal 

 size, the finer branches being directed rostrad (fig. 51) and the 

 coarser branches caudad. From this it follows that the ascend- 

 ing VIII root fibers are all of fine calibre, while the descending 

 fibers are partly coarse and partly fine. 



A considerable number of VIII root fibers pass directly medial- 

 ward in the marginal zone of the gray substance and apparently 

 decussate in the ventral commissure, but I have not been able 

 to determine their ultimate distribution. 



The general cutaneous roots of the V, VII, and IX nerves. The 

 trigeminal fibers of this system arise from neurones of the semi- 

 lunar or Gasserian ganglion. This ganglion is composed of neu- 

 rones of various sizes, large, medium and small, all of which so far 

 as observed are unipolar (fig. 45). The larger cell bodies are 

 connected with the larger root fibers. 



Some details of the mode of termination of the collaterals of 

 the V root fibers are seen in figure 49. Golgi preparations show 

 further (fig. 50) that the larger fibers of the sensory V root take a 

 deeper position within the oblongata before dividing into ascend- 

 ing and descending branches. The ascending branches (which 

 are of smaller calibre than the descending and in the adult are 

 unmedullated) pass forward to the rostral end of the auricular 

 lobe (figs. 3, 6). The finer fibers of the sensory V root also bifur- 

 cate into ascending and descending branches and take a more 

 superficial position in the oblongata. The descending branches 

 of these fibers throughout the length of the spinal V root are 



