Herri CK, Cerebrum of the Opossum. 15 



confines of a clustre of Deiter cells. Within the cortex there are ir- 

 regularly disposed sensory cells. It will be observed that the post- 

 rhinal lobe lies in or near the anterior perforated area. Comparing 

 the mammal brain with that of Sauropsida, it seems legitimate to con- 

 clude that these sharply localized clustres of corpuscles correspond to 

 the proliferating areas of the axial lobe of the reptiles and birds. The 

 presence of great numbers of vessels is essential for this purpose. The 

 opaque color of the region in which the corpuscles are imbeded may 

 be accounted for by the supposition that albumenous matter is collect- 

 ed about the proliferating centres. May it not be that those cells 

 which are so uniformly associated with the large end of the pyramid 

 cells of the cortex are derived from this or some similar source? In 

 this case, we have a novel modification of phagocytosis in the brain. 



In the caudad portion of the post rhinal lobe, especially ventrad, 

 the cell clustres and granular areas are especially numerous. The 

 third portion of the section consists of the pyriform lobe, which at this 

 level is similar in outline and size to the olfactory. The laterad, 

 caudad and mesad are provided with a strong sub superficial zone of 

 cells to be described more at length beyond but there is also a consid- 

 erable admixture ventrad and mesad of the rhino-morphic cell type. 

 In the central part of the pyriform lobe are numerous clustres of Deit- 

 er cells within clear spaces of the neuroglia, reminding one of those 

 clustres or rosette-groups of cells found in similar regions of birds and 

 reptiles. 



The cortex of the regions ventrad of the rJiinalis fissure has a habitus 

 of its own. Immediately beneath the neuroglia layer the cortex is 

 densely massed with only sparse pyramidal cells scattered entad with- 

 out the stratification encountered in the dorsal cortex. The cells of 

 the superior dense layer vary astonishingly in form, some being regu- 

 lar pyramids while the greater number are multipolar with numerous 

 processes which pass into the neuroglia zone and there break up into 

 a fine reticulum or felting of fibres which cannot in these sections be 

 seen to anastomose or to enter the superficial tracts (radices of olfac- 

 tory or otherwise). The deeper cells are chiefly pyramids and are fre- 

 quently so isolated as to appear beautifully distinct. (Fig. 7, Plate C.) 

 The apical process is generally peripheral and can be traced into the 

 neuroglia zone where it can be seen in many cases to break uj) into 

 numerous fine branches. The cell body is elongate pyramidal with 

 numerous lateral and basilateral branches which subdivide and weave 



