Herrick, Morphology of Nervous System. i^i 



the optic lobes. The histological structure, position of the 

 optic tracts and mesencephalic nidulus of the fifth nerve, etc., 

 make the identification certain. 



The diencephalon is not usually conspicuous, though 

 quite obvious dorsad in the gars. As though to compensate 

 for this limitation, the veiitral portion is highly developed, 

 and from the lateral aspects of the infundibulum two pouches 

 are formed, apparently without direct homologues in higher 

 brains, though possibly having some relation to the mam- 

 millare. Hypophysis and epiphysis have the usual form and 

 position, and in histological structure vary but little from the 

 reptilian type. 



The cerebellum is enormously developed, standing in 

 relation with the relatively large size of the axial lobes of the 

 cerebrum. The extended work of Miklucho-Maclay has done 

 much to prevent a true understanding of the relations, espe- 

 cially when accepted by Gegenbaur. Overlooking the thala- 

 mus entirely, he identifies the optic lobes as the diencephalon 

 and designates a part of the cerebellum as optic lobes, the 

 rest as cerebellum, and the posterior part of the medulla as 

 " nachhirn." 



As will be gathered from what follows, the minute struc- 

 ture as well as the position of the commissures, etc., settle 

 the homologies in most respects quite decisively. 



Our present purpose requires specific reference to only the 

 following papers, which have chiefly influenced the synon- 

 omy employed. (See end of this article for bibliography.) 



Wilder, B. G. On the Brains of Fishes. Proc. of the Acadcmx 

 of Natural Sciences of Philadelphia, 1S76, pp. 51—53. 



Wilder, B. G. Proc. Aw. Assoc. Adv. of Sciences for 1S75. 



Sanders, A. Contributions to the Anatomy of the Central Ner- 

 vous System in Vertebrate Animals. Part I, Section i, Sub-section i — 

 Teleostei. Pl/ilos. Transactions. 1S78. (This paper gives summary of 

 literature prior to 1879.) 



Alhorn, F. Untersuchungen iiber das Gehirn der Petromjzonten. 

 Zeitsch. f. ti'iss. Zoologie^ XXXIX, pp. 192-294, 1883. 



N. GoRONOWiTSCH. Das Gehirn und die Cranialnerven von Aci- 

 penser ruthenus. Morfli. yahrhiir//., lid. XIII, iSSS, pp. 427-574. 



