INTERPEDUNCULAR NUCLEUS 199 



notably in the formation of glomeruli. Most of them end in the rostral 

 half of the interpeduncular neuropil. 



Tradus olfacto-pedujicularis. — This important component of the 

 basal forebrain bundles (fig. 101; 'SOb, p. 534, figs. 1, 57), after con- 

 tributing fibers to the hypothalamus and peduncle, continues spinal- 

 ward along the lateral border of the specific interpeduncular neuro- 

 pil. The endings of these fibers are similar to those of tr. mamillo- 

 interpeduncularis (figs. 18, 19, 21, 25-30, 53, 54, 59, 72, 82). This 

 tract in the interpeduncular region lies laterally and dorsally of tr. 

 mamillo-interpeduncularis, extending spinalward beyond the pos- 

 terior end of the interpeduncular nucleus. There are some terminals 

 of both this and the preceding tract in the dispersed interpeduncular 

 neuropil. 



Nervus terminalis. — In Necturus the longest fascicles of this nerve 

 root probably reach the interpeduncular neuropil ('34c, p. 124). In 

 Ambly stoma a small fascicle was observed by McKibben ('11, p. 

 270) to reach the "dorsolateral part of the hypothalamus and the in- 

 terpeduncular region." Some of these fibers may connect with the 

 interpeduncular nucleus, but this has not been demonstrated. 



Tradus tegmento-ititerpedimcularis. — This is a very extensive con- 

 nection, which takes two forms. There is, first, a system of short axons 

 dispersed in the neuropil of the gray and the deep neuropil of the 

 alba which arise from small cells of the dorsal, isthmic, and trigeminal 

 tegmentum and descend directly to the interpeduncular neuropil. 

 Some may come from the tectum. They are especially concentrated 

 in the f. tegmentalis profundus (p. 286). A second type of connec- 

 tion is made by collaterals of the thicker axons of tr. tegmento- 

 bulbaris at their decussation in the ventral commissure. 



1. The short tegmento-interpeduncular fibers of the first grouj) are 

 unmyelinated. Their general arrangement is well shown in the sagit- 

 tal sections, figures 79 and 80. They arborize in the neuropil of the 

 gray of the interpeduncular nucleus and at all depths of the neuroj^il 

 of the alba, forming an important component of the diffuse neuropil. 

 Transverse sections show that, in addition to the diffuse spread of 

 these fibers in the neuropil, there are also tufted endings which form 

 part of the axonic component of the glomeruli (figs. 61, 62, 63, 66, 

 84). 



2. The tr. tegmento-bulbaris cruciatus as described in the larva 

 ('396, p. 590) is a series of thick axons of large cells of the isthmic and 

 trigeminal tegmentum, which decussate dispersed in the ventral 



