Herrick, Cerebrum of the Opossum. 13 



the ectal layer. Into this felting pass the apical fibres of the pyramids 

 of the smaller size or ectal series. It is not easy to trace the ultimate 

 course of these fibres, but m some cases, at least, they obviously di- 

 vide into two and are lost in the neuropilem above referred to. Be- 

 neath the small pyramids at a variable distance is an ill-defined layer 

 of larger pyramids whose apical processes seem also to pass into the 

 neuropilem. Still entad of the giant pyramids are the usual multipolar 

 cells adjacent to the white mater or fibre zone. More or less frequent 

 in all of these layers, but especially eatad, are large clear granular 

 nuclei surrounded by unstained spaces which may represent the bodies 

 of unstained cells of the aesthesodic type. In cases where the cell- 

 body is stained it almost invariably has the apical process directed en- 

 tad. The average length of the body of the small pyramids is about 

 .03 min., while the giant pyramids are more than .04 min. e.xclusive 

 of processes. 



The cortex of the crus, i. e. of the lateral aspects of the cerebrum 

 below the rhinalis fissure is the same as that of the ventral part of the 

 cortex farther caudad. 



Longitudinal perpendicular sections exhibit little difference be- 

 tween the cephalic and caudal portions of the dorsal cortex although 

 the latter portion seems to possess proportionally more of the second 

 type of cells. 



In a section of the parietal region the neuroglia layer consists of an 

 outer less densely stained layer and an ental layer which latter is suffused 

 with stained matter evidently of an albumenous character. The in- 

 ner layer may be called the ectal neuropilem zone because of its be- 

 ing filled with the finely dividing process of layers within. The an- 

 astamosis of these fibres, while very probable, has not been observed. 

 The cellular elements in this layer are inoblasts of connective 

 fibres and Deiter's cells. Beneath the neuroglia is a band of cells 

 forming the ectal portion of the cell-bearing cortex. The cells are 

 small pyramids in part but a careful study shows that there are many 

 cells of a somewhat different charactef, i. e. the peripheral process is 

 not simple but branches dichotomously and then subdivides into a fine 

 fibrilary felt. Immediately above and about this layer the felting of 

 fibres is most dense and results frequently in a diffuse coloration rend- 

 ering observation difficult. Beneath this layer there follow successive 

 layers of small pyramids with some fusiform cells. The fibres from 

 the apex in each case is continued to the ectal neuropilem zone there 



