66 journal of Comparative Neurology and Psychology. 



of these fibers in the velum, and it may be that the large cells of 

 the tectum are related directly or indirectly to this tract, which I 

 have called the tr. tecto-cerehellaris superior to distinguish it from 

 a part of the commissura ansulata fibers which also form a cere- 

 bellar connection. This nucleus magnocellularis tecti has been 

 generally considered as the place of origin of a mesencephalic 

 radix trigemini, from the time that Burckhardt described it as 

 such and homologized it with a nucleus which in higher verte- 

 brates is found laterally of the aquceductus Sylvii and gives rise 

 to the tractus trigemini. That the nucleus magnocellularis tecti 

 forms the nucleus of a radix quinti I cannot believe. At least I 

 am not able to advance any proof for it, but can adduce two points 

 against it. The first is the nonexistence of this nucleus or of such 

 a root in the teleosts, in which the trigeminus is at least as strongly 

 developed as here. In the second place, I have been able to 

 recognize those fibers which have been described as the tr. quinto- 

 tectalis by Edinger as being in no relation whatever to the tec- 

 tum. I shall have more to say about this tract in the next chap- 

 ter. 



Regarding the commissura posterior, I have already mentioned 

 that its most anterior part is provided by fibers originating in the 

 deep layer of the tectum, while the second part, which is the strong- 

 est, begins in the median subventricular substance, and both end 

 in this substance of the opposite side, as has been described for the 

 teleosts. Farther backward the fibers decrease in number and 

 now^ pass more directly caudad and at a little distance in front of 

 the origin of the fasciculus longitudinalis dorsalis they divide into 

 fine bundles which evidently terminate there. This is the reason 

 why I cannot believe that either here or in the teleosts the com- 

 missural fibers pass into the fasc. long, posterior. But the fibers 

 of this fascicle begin in the same group of cells in whose anterior 

 part the fibers of the commissure terminate, from which it follows 

 that an indirect relation between these two systems is more than 

 probable. 



The dorsal longitudinal fascicle first appears as thick, strongly 

 medullated decussating fibers which increase greatly in number 

 near the nucleus of the oculomotorius. It then runs backw^ard 

 into the oblongata under the ventricle close to the raphe. 



Three other tracts must be described here, of which only one 

 passes out of the mid-brain, the others terminating w^ithin it. 



