142 Cincinnati Society of Natural History. 



way of the fornix to the calloso-marginal region. It is uncertain 

 whether the fibres from this region to the taenia thalami have any- 

 thing to do with the olfactory tract, though this is not excluded by 

 observation. 



3. Microscopic structure of the cerebrum. The natural division of 

 the cerebrum into an axillary and mantle portion, is likewise very 

 convenient for the purpose of description of the nervous elements. 

 Attention is again called to the reason for regarding these two 

 regions more closely related than either is with the diencephalon. 

 The corpus striatum, as such, does not exist in the alligator, but 

 the major part of the cerebrum consists of what Rabl-Rueckhard 

 called axillary lobes (Stammlapfen). The axillary lobes consist of 

 a rather homogeneous mass of cells, and has a contour similar to 

 that of the entire hemispheres, but is covered by a mantle which 

 embraces it on all sides except behind, and is separated from it 

 on all sides except antero-inferiorly by the ventricle, which is 

 exceedingly narrow. The axillary lobes are, therefore, the imme- 

 diate cellular envelopes of the direct extension of the peduncle?. 

 The mantle portion is exceedingly thin, and presents little oppor- 

 tunity for variety in structure. There is, however, a marked 

 diversity in the cellular elements entering it, as will be gathered 

 from descriptions of the sections. 



Three distinct kinds of cells can be detected in the mantle ; one 

 characteristic of the superior and anterior regions, another of the 

 occipital, median and posterior-lateral regions, and a third about 

 the ventro-basal regions or hippocampus. From analogy these 

 may be assigned to motor, psycho-sensory and special olfactory 

 functions respectively. The axial lobes likewise have two sorts. 



The pyramidal cells which were first above mentioned, stain 

 deeply, have small nuclei, and have a long apex-process generally 

 directed obliquely toward the periphery, and several basi-lateral 

 processes. No central basal process such as described by Meynert 

 was seen. These motor cells can be traced into connection with 

 the basal prosencephalic tract (continuations' of the peduncles). 

 Indeed, similar cells can be followed to the diencephalon. The 

 second variety of cells is flask-shaped or balloon-shaped, and has a 

 slight power of precipitating stains ; and is further characterized by 

 the large clear nucleus or perinucleary space. Such cells are dis- 

 tinctive elements over the posterior and median parts of the cortex. 

 Especially constant are they in the median wall. (Fig. 9, Plate 



