76 BULLETIN OF THE LABORATORIES 



rated laterad by the rhinalis fissure and mesad by the splenialis. The 

 portion dorsad of these almost continuous fissures may be regarded as 

 the dorsal lamina or mantle par excellence, while that part beneath 

 contains the ventral lamina and alae. A large part of the ventral por- 

 tion is devoid of cortex in the usual sense. The dorsal surface is 

 divided into a small frontal lobe, which is circumscribed very deeply 

 from the rest, and a large ovate parieto-occipital portion, which is not 

 subdivided. 



The ventral portion is likewise divided into an anterior post-rhinal 

 lobe occupying the region in front of the chiasm and fusing with the 

 crus cephalad, and the large pyriform lobe with its modified cortex. 

 The latter is expanded by the ventral part of the hippocampus into 

 which it passes caudo-ventrad. 



The sylvian fissure is not pronounced and does not extend across 

 the rhinalis fissure. A slight longitudinal depression extends longitu- 

 dinally of the pyriform. This marks the course of the olfactory fibres 

 and limits the non-cortical from the cortical portion. All of the region 

 ventrad is devoid of a genuine cortex. Dorsad of it, the surface is 

 occupied by olfactory fibres as far as to the rhinalis fissure. The 

 mesad surface is separated by the splenialis or calloso-margmal fissure 

 into a dorsal and ventral portion, but this fissure is relatively farther 

 dorsad than the rhinalis by reason of the interpenetration of the thala- 

 mus. Cephalad, the rhinalis and splenialis unite and cut off the pro- 

 jecting frontal lobe from the crus beneath. 



There is a slight fissure where one might look for the callosal, but 

 in the absence of that commissure it is but the union of the cortex of 

 the gyrus fornicatus with the base. All beneath this fissure is devoid 

 of true cortex and is continued caudad into the septum and corpus 

 fornicis. (See Figs. 3 and 4, Plate A.) The splenialis grows deeper 

 as it passes caudad, following the arch of the hemisphere until it lies 

 in a dorso-ventral line. By comparing the longitudinal sections of 

 Plate B with the transverse series of Plate A, the course of the fissure 

 and the structure of the hippocampus will be perfectly obvious. The 

 commissures are discussed beyond. 



The thalamus is about as in rodents. 



Minute Anatomy. 

 R]iijicnccpJiaIon. The olfactory lobe, as a whole, is of relatively 

 very large size, being expanded in all directions beyond the crus and 

 especially produced eephalo-dorsad. No part of the dorsal part of the 



