Herrick, Morphology of Brain of Bony Fishes. 39 



uncle is passing into the hypoarium and the mammillare contains 

 a closed chamber, recessus infundibuli posterior. 



The commissural systems of the chiasm region are crowded 

 apart in Dorosovia by the enormous development of the optic 

 nerves and chiasm, so that they are very completely distin- 

 guished. Fig. 8, Plate XXI, Vol. I, gives a good idea of the rela- 

 tions at the point where the ventral and dorsal portions of the optic 

 tracts are separating. In the narrow isthmus between the optic 

 tracts the peduncular tracts and a part of the commissural 

 tracts, are closely crowded. At e — broken in the plate, but 

 next above vent. Ill v. — is the point of crossing of commissura 

 horizontalis. Above it, at d, are tracts from the commissura 

 minor which a few sections caudad passes sharply laterad to the 

 cell layer above the ventral optic brachium, as in all other cases. 

 It is followed cephalad a long distance and decussates above the 

 commissura transversa in the limited area behind the chiasm. 

 There is some suggestion of a decussation, however, and the 

 question is perhaps not to be decided without a more complete 

 series of this species. On either side, adjacent to the ventral 

 optic brachia, is the obliquely cut portion of the commissura 

 transversa, between which and d is the ventral peduncle bundle, 

 while dorsad of it, at /;, is the dorsal peduncle which becomes 

 distinct farther caudad. On the right side of the figure, above 

 the nidulus/, is the tuber tract to the ventral commissure, which 

 crosses in a section cephalad. A short distance caudad the 

 ventral peduncle turns directly ventrad so that its entire course 

 can be traced from ihe thalamus to the ventro-lateral region of 

 the tuber near the hypoaria, into which, the fibres enter. 



According to Edinger, the commissura transversa is proba- 

 bly a decussation. "Sie durchzieht fast die ganze Breite des 

 infundibulums, und es wenden sich nahe der lateralen Ausen- 

 fliiche ihre Fasern riickwarts und aufwarts um sich im hinteren 

 Bereich des Mittlehirnes nahe dem Dache dann der weiteren 

 Beobachtung zu entziehen." He compares it to Meynert's 

 commissure of mammals. 



It appears that no homologue of the commissura horizon- 

 talis has been found in Selachii by Edinger. 



