10 C. JUDSON HERRICK 



fibers curve downward and backward, here coming into relation 

 with the coarse fibers of the mesencephalic V root, and then spread- 

 ing out in the floor and posterior walls of the lateral recess {com.cb., 

 figs. 5 to 8, 17, 27). None of these fibers leave the substance of 

 the cerebellum, so far as revealed by Weigert preparations. 



The determination of the exact relations of the root fibers of the 

 trigeminus to the cerebellum is very difficult, and I have not 

 as precise information on this point in Necturus as in larval 

 Amblystoma. In the latter type I have found that practically 

 all fibers of the sensory V root bifurcate immediately upon en- 

 tering the brain, theu' ascending branches extending forward to 

 the rostral end of the auricular lobe. Probably the same holds 

 for Necturus, but there is no evidence that any of these fibers 

 reach the cerebellum in Necturus. 



The connections of the mesencephalic root of the V nerve in 

 Necturus have been described by Osbom ('88), Kingsbury ('95), 

 Johnston ('05) and Norris ('13). The two authors first men- 

 tioned have commented upon the fact that the mesencephalic V 

 root is accompanied by a tract of coarse meduUated fibers which 

 can be followed caudad from the level of the superficial origin of 

 the V nerve as far as the roots of the VII and VIII nerves, lying 

 dorso-medially of the spinal V tract. Norris ('13, p. 269) de- 

 scribes in Siren a portion of the mesencephalic V root which 

 descends from the superficial origin of the root "as far poste- 

 riorly as the level of the root of the seventh nerve." I find in 

 Amblystoma that these coarse descending fibers arise by the bi- 

 furcation of the mesencephalic root fibers and end among the 

 cells of the motor VII nucleus. The details of this connection 

 will be described elsewhere. A similar condition doubtless pre- 

 vails in Necturus, and these are probably the fibers referred to 

 by Osborn and Kingsbury. 



The mesencephalic V fibers are, moreover, mingled with those 

 of a quite independent system of coarse medullated fibers. In 

 Amblystoma, where I have studied this tract more carefully, 

 its fibers have been followed forward into the post-optic commis- 

 sure. This makes it probable that it is a crossed descending 

 tract from the thalamus or midbrain and it is accordingly here 

 termed provisionally tractus thalamo-bulbaris. 



