Notes upon the Brain of the Alligator. 143 



VII.) The great bulk of the axial lobes — that portion which pro- 

 trudes into the ventricle — is filled with similar flask cells, but these 

 are curiously clustered in groups of two or multiples of two. 

 (Plate VII., Figs. 7, 8.) The evidence that these cells are under- 

 going rapid increase by fission in this young animal is very 

 conclusive. All stages of the process may be observed. It may be 

 suggested that, if in the case of young animals this part of the 

 brain is most actively multiplying cells, it is possible that the 

 growth of the mantle (in which there is little material for rapid 

 growth) may be in some way associated with this proliferation of 

 cells, resulting in the increase of the mantle from its margins, as 

 though the material were pushed up around the margins of the 

 ventricle by rapid growth within. 



The connection of this portion of the axial lobes of the cerebrum 

 seems to be with the superior or sensory longitudinal tracts of the 

 peduncles. In addition to the tracts above mentioned, the tsenia 

 thalami, springing from the basal region and passing to the habe- 

 nulae, form a sensory link between the thalamus and the cortex. It 

 is noticeable that the cells associated with this tract, even in the 

 thalamus, are of the flask variety. It is perhaps advisable to here 

 discuss the structure of the actual sections. 



Details of transverse sectio7is of the hemispheres . The description 

 already given, with the figures of Plate VIII. , will sufficiently 

 illustrate the relations of the ventricles, etc. The cellular structure 

 of the cortex varies little from section to section. There are four 

 regions, each with its typical form of cell, visible in cross sections 

 of the anterior and median parts of the hemisphere. The dorsal and 

 anterior portion of the median cortex contains pyramidal, irregular, 

 multipolar cells of the sort represented in Fig. n, Plate IX. The 

 whole lateral aspect is occupied by a dense layer of cells of nearly 

 the size, but of different appearance from the last. They resemble 

 those figured on Plate VII., Fig. 12, being rather flask-shaped, 

 with large nuclei and few processes. Although at one time sus- 

 pected that different axial position might account for the different 

 aspect, this seems unsupported by observation. 



A third cell-clustre, which occupies a relatively small area ante- 

 riorly, but increases caudad, occupies the lower median portion of 

 the mantle. It consists of flask-like or sensory cells with fibres 

 which can be traced to the tract leading directly ventrad to the 

 ventral median portion of the posterior part of the brain, /'. e., the 



