126 Journal of Comparative Neurology 



fibres of the olfactory nerve); second, we come to the so-called 

 glomerulary layer where are probably manufactured the myeline 

 sheaths of the nerve-fibres and where the terminal dendrids of 

 the fibres of the olfactory nerves enter into relations with those 

 of the protoplasmic processes of the cells of the next, or 

 ganglionic layer ; third is found the ganglionic layer of pyra- 

 midal cells whose axis cylinder processes unite to form the radices 

 lateralis and mesalis. The fourth and last layer of the pero 

 consists of dense stratified granules. The pes consists of small 

 fusiform cells like those of the hippocampal lobe, which goes 

 to prove its central origin. It is from this layer that the large 

 and circular bundle of radix entalis arises. 



From these two portions of the olfactory bulb arise three 

 bundles of fibres which pass backward, and in the case of two 

 of them, at least, into certain definite relations with the hippo- 

 campus, and whose course is the occasion at present of so much 

 discussion. The largest of these bundles, known as the radix 

 lateralis from its position on the lateral aspect of the tuber, 

 arises from the pero, or the outer layer. This bundle has been 

 traced with comparative accuracy back to its cerebral connec- 

 tions in the hippocampus. The fibres of the radix lateralis 

 gather in the granular layer of the pero, about the tip of the 

 ventricle and on the ventral aspects of the tuber; pass ectad 

 along the outer surface, spread out over and dip into the hippo- 

 campal region. They connect here with the ectal region of the 

 hippocampal lobe. The radix mesalis, so called because it 

 arises on the inner aspects of the tubers, and thus approximates 

 the median line, has been traced into the indusium, the so- 

 called striae Lancisii, (Fish, No. 7.) It arises from the pero. 

 This bundle is small as compared with the outer radix later- 

 alis and is not so compact, being dispersed over the in- 

 ner and ventral aspect. It has been found to pass to the 

 gyrus fornicatus in the opossum, which is the cephalic 

 part of the hippocampus. Beyond this its fibres have not 

 been traced with any degree of certainty. The fact is here to 

 be noted that the radix lateralis arising from the lateral aspect 

 of the pero ends in the hippocampus without any morpholog- 



