MEDULLA OBLONGATA 169 



a return path from the tectum to the visceral-gustatory nucleus by- 

 way of tr. tecto-bulbaris rectus — a typical reflex circle (p. 76). 



At the outer border of the gray of this nucleus, in a few prepara- 

 tions there are large spindle-shaped neurons, with dendrites extend- 

 ing for long distances tangentially to the gray layer. One dendrite 

 may ramify among terminals of the secondary visceral tract and 

 dorsal tegmental fascicles of groups (7), (8), and (9) and the other 

 in the deep neuropil and the f. tegmentalis profundus. One such ele- 

 ment is illustrated in figure 101, showing an axon directed dorsally 

 toward the decussatio veli, possibly a commissural connection be- 

 tween the two visceral nuclei similar to that described in the frog and 

 in fishes. 



These afferent connections suggest that this isthmic nucleus is a 

 correlation center, where gustatory, general visceral, and a consider- 

 able variety of other types of experience are brought into relation, 

 with the gustatory component dominant and all in the interest of 

 reflexes concerned with feeding. The afferent fibers of the secondary 

 gustatory tract terminate not only in the neuropil of the visceral- 

 gustatory nucleus but also in that of the adjacent isthmic and dorsal 

 tegmentum ('25, fig. 19; '42, fig. 43), where reflexes of the jaw and 

 hyoid musculature are believed to be organized (p. 190). 



This hypothesis is supported also by the courses taken by the ef- 

 ferent fibers. These go out in several directions. First, there is a dis- 

 persed group of fibers which spread in the underlying tegmentum 

 (figs. 8, 13). This is a direct connection with the neuromotor appa- 

 ratus of the mouth and pharynx. The remainder enter the tertiary 

 visceral tract (fig. 8, tr.v.t.), which has rather wide distribution. This 

 tract of Amblystoma is relatively small, and its fibers are dispersed 

 and so intimately mingled with others that analysis is difficult. The 

 diagrams show what has been clearly seen. In figure 8 the dotted 

 component of tr.v.t. is highly probable, though not confirmed by 

 elective impregnations. 



In the description of the brachium conjunctivum (p. 176) this 

 fascicle is shown to descend close to the gray in the posterior lip of 

 the isthmic sulcus to reach the decussation. In this part of their 

 course the cerebellar fibers comprise a large component of the f . teg- 

 mentalis profundus. As they emerge from the cerebellar formation, 

 they pass through the superior visceral nucleus, and here they are 

 joined by a smaller number of similar thin unmyelinated axons of 



