232 C. JUDSON HERRICK 



posterius, though here the boundary between the two structures 

 is more clearly marked by a very broad depression, which may 

 also represent a portion of the sulcus limitans. 



The floor of the wide infundibulum in the mid-ventral plane 

 is thin but nervous, containing a large tract of unmyelinated 

 nerve fibers related with the pars infundibularis of the hypo- 

 physis. The roof of the infundibulum is also thin but nervous, 

 containing a large number of unmyelinated nerve fibers which 

 ramify throughout the saccus vasculosus. This is a convoluted 

 epithelial structure which forms the more posterior part of the 

 roof of the infundibulum (fig. 62, sac.v.). Attached to the 

 caudal end of the infundibulum is the very large glandular part 

 of the hypophysis (fig. 62, hyp.g.). 



In this article we shall not attempt a systematic exposition 

 of the functional connections of the diencephalon. Its mesen- 

 cephalic connections will be described and other diencephahc 

 tracts will be mentioned only incidentally or not at all. 



General histology 



The walls of urodele brains are seen in section to be sharply 

 divided into a deep stratum griseum or ventricular gray, and 

 a superficial stratum album. In ordinary histological prepara- 

 tions the cells of the ventricular gray appear to be similar, save 

 for the presence of occasional groups of larger cells and for an 

 obscure lamination in some parts of the brain. 



In Necturus neither the walls of the brain tube as a whole 

 nor their two layers are of uniform thickness throughout. The 

 thickening of the wall may be due to the presence in the stratum 

 album of long fiber tracts connecting remote parts, as in the 

 cerebral peduncle, or to a more active functional differentiation 

 locally. In the latter case the stratum griseum will be thick- 

 ened as a result of an increase in the number of cell bodies of 

 the contained neurons, and this thickening in general first takes 

 the form of a projection into the ventricle rather than outward 

 into the stratum album. The eminences thus formed on the 

 ventricular surfaces of the brain are, therefore, of great value 



