52 



In Sauropsida (according to Spitzka, Brill and Edinger among 

 others) the hippocampus even crosses the dorso-mesial edge to form 

 part of the dorsum of the cerebrum. Thus as the animal scale is 

 descended the hippocampus and the pyriform approach one another 

 on the lateral aspect of the cerebrum. Brill even goes so far as to 

 infer that they meet. In other words the "pallium" virtually dis- 

 appears in the Sauropsida. According to Meyer also no "pallium" 

 (in the sense used here) exists in Submammalia. Whether this be 

 true or no, this much is certain that the pyriform lobe is closely 

 related to the hippocampus in the whole of its extent among certain 

 lowly Vertebrates. In lower Mammals pallial tracts are "added" 

 (Edinger) to separate the pyriform from the hippocampus except at 

 their caudal extremities, where the former overlaps the latter. Now 

 as the caudal part of the hippocampus is all that is left in Eutheria 

 of the Metatherian hippocampus, it happens that the pyriform lobe 

 (hippocampal convolution) is adjacent to the hippocampus. But the 

 study of the non-placental Mammalian brain shows that this relation- 

 ship is not essential, but probably only fortuitous. 



The tuberculum olfactorium and precommissural area (the portion 

 of the "septum lucidum", of most writers, which lies in front of the 

 thickened lamina terminalis resemble one another in that they con- 

 tain small scattered polyhedral cells, with none of the typical cortical 

 arrangement. Into relation with these cells large numbers of medullated 

 fibres coming from the olfactory bulb terminate, in a similar manner 

 to which the fibres of the external olfactory radiation terminate in 

 relation to the cells of the pyriform lobe. The axis-cylinder processes 

 of these cells form an important share of Zuckerkandl's Riechbiindel 

 (the precommissural fibres of Huxley), running upwards in the pre- 

 commissural area and septum lucidum to the hippocampus. These 

 fibres are intimately mixed with a number of fibres proceeding by the 

 same route from the hippocampus to the base of the brain. Arising 

 in the olfactory bulb, apparently in a similar manner to the other 

 "radiations", there is a diffuse fibre tract, which, following the nomen- 

 clature of Zuckerkandl I have already distinguished as the "olfactory 

 bundle of the fascia dentata" (Anat. Anz,, Bd. X, No. 15). 



The olfactory peduncle, tuberculum olfactorium and pyriform lobe 

 are closely connected with the other hemisphere by means of the 

 anterior commissure. The precommissural area is connected with the 

 other side by a part of the hippocampal commissure, which Herrick 

 calls "corpus callosum". 



By means of a very strong fibre system situated in the substance 

 of the tuberculum olfactorium and in series with the internal capsule 



