Herkick, Morphology of Brain of Bony Fishes. 341 



these two portions are essentially different and have unlike 

 connections, and the structure of the olfactory of fishes but 

 strengthens an opinion primarily based on a study of Saurop- 

 sida and maiTimals.(') In serpents it was shown that that 

 so-called olfactory tract Which crosses in the anterior com- 

 missure is derived from the pes or cerebral part of the bulbus, 

 while the radix lateralis is derived from the true olfactory or 

 glomerulary structure, and it terminates in the homologue of 

 the hippocampus or adjacent structures. This appears to be 

 equally true of the fish, and the destination of the several 

 tracts is much more distinctly made out than in any other 

 group. 



The pero consists of a dense investment of fibres which 

 lie in greatly confused strands about the glomerular layer, 

 not unlike that of all higher animals. Within the glomerular 

 zone is an irregular layer of specific olfactory cells, which are 

 unusually large and irregular (Plate XXV, Fig. i). These 

 cells are multipolar, with several long processes beside the 

 one which enters the nerve fibre. The nuclei are small and 

 spherical and unstained. The proximal fibres derived from 

 this layer collect at the lateral aspect as a large and very dis- 

 tinct radix lateralis. 



The core of the olfactory, or pes proper, is filled with a 

 small type of fusiform cells, not unlike those of the hippo- 

 cam pal lobe. From this there obscurely arises the large 

 circular bundle of the radix mesalis. The subjoined account 

 from Sanders may be taken as applying pi'etty well to the 

 case in hand:(^) 



" The lobi olfactorii consist essentially of three layers. Of 

 these the external is thicker in front, and is formed by the 

 fibres of the olfactory nerve, which in entering diverge in all 

 directions and form a sort of envelope for the anterior part of 

 the lobe. More internal comes a layer of iinely granular 



1 C. L. Herrick, " Topography and Histology of the Brain of Certain Reptiles," 

 Journal of Comi'arative Neurology, p. 24, 1891. 



2 "^AVD'-RR " Contr. to the Anatomy of the Central Nervous System in Vertebrate 

 Animals," Subsection i, Teleosiei. Philos. Trans., p. 748. 



