Notes upon the Brain of the Alligator. 141 



angular form, deep staining, and prevailingly peripheral direction of 

 the apical processes, as well as the relatively small but variable size 

 of the latter, are the most important features. In mammals the 

 ganglion cells are pyramidal, with irregular bases toward the per- 

 iphery, and with long, apex processes directed centrally. The 

 structure of the olfactory, lobes in lower vertebrates merits more 

 study. (Compare Bid. Denison University, Vol. V., for figure of 

 corresponding structure in Arctomys.) Within the narrow zone of 

 ganglion cells is a homogeneous belt, with only scattered cells, sep- 

 arating it from the mass of more or less concentrically arranged 

 cells making up the bulk of the centre of the bulb. The large ven- 

 tricle is clothed with deeply staining epithelium. (Plate IX., Figs. 

 6 and 6a.) 



A peculiarity worthy of notice is the existence of a remarkable 

 olfactory fossa, which does not appear superficially, but is readily 

 seen in longitudinal median sections of the bulb, in which it 

 appears as a pit-like depression of the ganglionic layer, filled with 

 a special mass of the glomerular zone, and which is connected with 

 the fibre layer by a special tract. 



The inner nucleary mass extends some distance into the crura, 

 but is then supplanted by a cell-structure like that typical of the 

 cerebrum. In fact, two cerebral elements enter nearly simulta- 

 neously. The pyramidal deeply-staining elements predominate, 

 while the flask-like pale cells are generally nearer the center than 

 the others, or occupy a median position with reference to the com- 

 bined crura. The longitudinal axes of these two varieties of cells 

 are not parallel, even in the crura. All evidence of special olfactory 

 structure disappears long before the union of the latter with the 

 hemispheres. As the crura approach the cerebrum the olfactory 

 fibres collect in the lower portion, and the region becomes per- 

 meated with minute multipolar or bipolar cells like those which 

 occur in the hippocampal region of higher vertebrates. These 

 stain deeply, and are very irregularly distributed. The olfactory 

 fibres gather in the lower median angle as the tract passes into 

 hemisphere, and they can be traced in one tract candad and dor- 

 sad to about the level of the anterior commissure, whence it may 

 be conjectured that fibres proceed to the cortex of the calloso-mar- 

 ginal or occipital region. It is probable that other and important 

 parts of the tract are superficial on the inferior and lateral basal 

 areas collecting at the postero-basal margin, and sending fibres by 



