56 Journal of Comparative Neurology. 



X . — The pes pedunciili. 



I. The hypoaria, which afford the most characteristic 

 pecuHarities of the fish-brain, have been interpreted in vari- 

 ous ways. Haller called them " olfactoria inferiora " or " tu- 

 bercula reniformia." Cuvier called them " lobes oj^tiques," 

 while Mayer compared them to a combined thalamus and stri- 

 atum. Hollard regarded them as the specific equivalent of the 

 striata, basing the opinion on the observation (the correctness of 

 which was denied by Vulpian) that the peduncular fibres from 

 the corona radiata terminate in their substance. It is only neces- 

 sary to refer to the view of Girgensohn, that the two hypoaria 

 constitute a modified hypophysis, as the hypophysis is easily dis- 

 covered in any fish. Carus considered them the equivalent of 

 the tuber cinerum, while most recent writers, including Fritsch 

 and Sanders, seem to incline to look upon them as more or less 

 specific homologues of the mammillary bodies or albicantia. 

 Stieda, with characteristic caution, refrained from too definite a 

 reference, but Fritsch is very positive in claiming that "The 

 lobi inferiores, in spite of their enormous extent, have no more 

 complicated structure than the corpora albicantia. The organi- 

 zation of these organs is related and supports the. homology as 

 does the external form and position."' This author claims that 

 the hypoaria resemble the albicantia in the fact that multipolar 

 ganglion cells of medium size resembling those of the cerebrum 

 occur in large numbers irregularly dispersed in a neuroglia net. 

 "Moreover a system of fibres homlogous with the fornix 

 descends from the torus longitudinalis and, passing through the 

 corpus rotundus, enters the hypoaria and from the same body 

 a bundle emerges with a curved course and passing about the 

 corpus rotundus loses itself in the thalamus" (colliculus). 

 Sanders describes the cellular structure as follows : 

 "The parenchyma of the hypoaria is composed of finely 

 granular neuroglia, in which the ramifications of extremely small 

 fibres form a network of inextricable tenuity. In the neuroglia 

 bundles of nerve-fibres radiate from the posterior and upper side 

 in distinct and well-formed cords. The nerve cells occur 

 throughout the neuroglia scattered singly, but increasing in num- 



lUntersuchungen u. d. Bau des Fischgehirns, p. 24. 



