1 8 Journal of Comparative Neurology. 



matter are large cells which change their direction to correspond with 

 the direction of the tracts. This lateral area may have other functions 

 than the dorsal or ventral area, but what the functions difference may 

 be it is impossible to conjecture. 



The motor regions of the cortex are illustrated by Figs, i and 2, 

 of Plate C. Fig. i is a drawing made to a scale illustrating a strip of 

 cortex extending from beneath the giant cells nearly to the upper cell 

 layer. The region is in the fron to dorsal cortex near the median 

 fissure. The two drawings are part of the same strip of cortex, the 

 right end of No. i being near the dorsal surface. The forms vary 

 considerably, some of the cells being simply fusiform, others inverted 

 pyramids while there are a few aesthesodic cells among them. 



Fig. 2, is a camera drawing of the cortex from the deep pyramids 

 to near the ectal layer. The apex processes extend beyond the cor- 

 tex. The process of nutrition of the pyramids suggested elsewhere is 

 well seen here. Several of the carrying corpuscles are often seen at 

 the base of one pyramid. Fig. 4, Plate C, is a camera drawing of a 

 few of the deep pyramids or ^iant cells under the one-fifteenth 

 objective. 



The general conclusions growing out of this investigation are 

 briefly as follows : There is in the opossum a decided difference be- 

 tween the aesthesodic and kinesodic cell types. Regions known to 

 be sensory contain a large number of the type with clear round 

 nuclei. The delimitation of the areas is, however, very incomplete. 

 This agrees well with the results of experiments. The two classes of 

 cells are rarely unmixed in any area. In many cases at least the 

 cortex cells give off processes which divide in the so-called neuroglia 

 layer to form either a neuropilem or reticulum. It would seem that 

 a more or less connected reticulum of fibres directly supplied by the 

 cells is the simplest anatomical device which can in any way be asso- 

 ciated with unit states of consciousness. 



The probern of nutrition of the specific nerve cells is, we believe, 

 somewhat simplified by the suggestion that there are special prolifer- 

 ating centres in the brain base in which there are produced numerous 

 corpuscles like Deiter's cells which then migrate to the cortex and 

 convey nutriment to the cells. The small and frequently shrunken 

 bodies at the bases of pyramidal cells are interpreted as such nutrient 

 bodies from the sources indicated, one of which is the post rhinal lobe 

 near the substantia perforata anterior. With reference to the fact that 



