THE SYSTEMS OF FIBERS 287 



extensive tegmento-peduncular and tegmento-bulbar system of in- 

 ternuncials, passing obliquely from the tegmental to the motor field; 

 but fibers of various other systems are mingled with these. They 

 comprise important components of the periventricular, deep and in- 

 termediate tegmental neuropil, with a dorsoventral trend. At the 

 outer border of the gray they are especially numerous, and here some 

 of the components are fasciculated as anatomically separate tracts 

 for part of their courses. Other more dispersed components also are 

 named as tracts in cases in which their terminal connections are 

 revealed by elective impregnations. Many of these fibers decussate 

 in the ventral commissure in the tuberculum posterius and spinal- 

 ward of it through the medulla oblongata. In the midbrain and upper 

 rhombencephalon there are numberless short crossed and uncrossed 

 fibers, some strictly commissural between the tegmental fields and 

 larger numbers passing from the tegmentum obliquely rostrad or 

 caudad, with or without decussation, to other parts of the motor 

 field. 



The list below includes all the tracts which have been identified in 

 this complex, and in addition to these there are diffuse connections 

 through the neuropil with all neighboring regions. This summary is 

 based upon what has been seen in both Amblystoma and Necturus. 



Brachium conjunctivuni (p. 176 and fig. 10). — This is one of the 

 largest and most compact components of the complex, though rarely 

 impregnated in our material. From the cerebellum to its decussation 

 it accompanies the isthmic sulcus, as is well shown in figure 71. 



Tertiary visceral-gu.s-tatory tract (p. 169 and figs. 8, *23). — These 

 fibers accompany those of the brachium conjunctivuni and are indis- 

 tinguishable from them except in elective impregnations. 



Tegmento-inter peduncular and inter pedunculo-teginental fibers (pp. 

 199, 201 and figs. 19, 60-68, 79, 80, 83, 84).— These very numerous 

 fibers, passing in both directions between the interpeduncular nu- 

 cleus and the isthmic and trigeminal tegmentum, are diffusely spread 

 in the neuropil of the gray and the deeper layers of alba. 



Tractus tegmento-pedimcularis (p. 215 and fig. 18). — These fibers 

 pass from the dorsal and isthmic tegmentum to the peduncle, dis- 

 persed at all depths of gray and white substance. Some of them 

 decussate in the ventral commissure in the vicinity of the fovea 

 isthmi. They accompany similar fibers of tr. tecto-peduncularis 

 (fig. 24). 



