Herrick, Cerebrum of the Opossum. 5 



The greater part of this cortex pertains to the cms and may l)e there 

 considered. 



Crus olfactorius. The cms terminates in the pes obHquely, the 

 lateral and dorsal portions being longest. Ventrally it is chiefly made 

 up of the radices of tracts from the pero. There are three such fibre- 

 bundles ; the largest, or radix pedis lateralis, is an exceedingly strong 

 band, as in rodents. Its development stands in direct proportion to 

 that of the olfactory lobe and this, in turn, with that of the hippo- 

 campus. The fibres collect in the granular layer of the pero and then 

 about the ventricle, accumulating chiefly mesad and ventrad. On 

 entering the pes they encounter the invading cortex cruris and are 

 driven ectad, thence laterad superficially to the cortex cruris, where 

 they form a strong bundle passing caudad and somewhat laterad along 

 the fissura radicis to the lobus pyriformis, thence for the most part to 

 cross mesad and entad into the hippocampus, especially the fornicate 

 gyrus. The tract of the fibres caudad is not compact but they spread 

 out to some extent upon the pyriform. The fibres of this ectal olfac- 

 tory tract are in part overlapped by fibres of a different character. 



The radix pedis >?iesalis, on the other hand, is very small and dis- 

 perse. Its fibres, which arise on the ventral and mesal, as well as 

 especially in the meso-dorsal part of the crus, pass in the neuroglia 

 layer and remain ectad to the cell zone until reaching the neighbor- 

 hood of the splenialis fissure, where they cross to the gyrus fornicatus. 

 The bundles do not unite to form a single tract but remain largely iso- 

 lated from each other. 



There is no external indication of a radix pedis intermedins, but 

 we encounter a few bundles which apparently arise from the ventral 

 part of the crus and passing caudad through the substance of the lobus 

 post-rhinalis emerge mesad and ectad to unite with the bundles of the 

 radix mesalis on their way to the gyrus fornicatus. The fibres enter 

 the peduncular tracts in their dorsad course and pass through them. 

 As indicated above, the dorsal, lateral and mesal aspects of the crus 

 are covered by cortical masses. 



Thus far we have been dealing with tracts which undoubtedly 

 pertain to the olfactory pero or ganglion proper. Greater difficulty 

 arises in construing the so called ental olfactory tract (radix mesalis of 

 fishes.) Following suggestions arising from these studies, Mr. C. 

 Judson Herrick has investigated the relations of the cortex cruris to 

 the pero, in rodents. He arrives at the conclusion (Bui. Denison 



