266 Susanna Phelps Gage 



trance to the aula dips ventrad, separating the portse (Fig. 

 17), and gives off from its dorsal part the two paraplexuses 

 (Fig. 42) which extend even into the rhinocceles. Dorsad of 

 the callosum it is constricted but continues caudad into the 

 diacoele (Fig 22) where it becomes much expanded and falls 

 into the infundibulum. 



Mesencephal. — There is no marked stricture between the 

 mesoccele and the diacoele though the postcommissure and 

 the origin of the 3d nerve may be considered as approximately 

 determining the division. 



Ventrad of the postcommissure are seen cells differing in 

 character from any others of the endyma, having a wide clear 

 margin, and together forming in section, a lunular mass on 

 either side (Fig. 59, 60, 9, 10). From these cells fibers appear 

 to take origin which become incorporated in the po.stcom- 

 missure. Sections prepared by the silver method were de- 

 fective in this region and hence proof of the connection of 

 the fibers with the cells is not positive. 



In lamprey (Fig. no), similar cells are found but the masses 

 are farther separated by the postcommissure. To the cells 

 similar in appearance, but underlying the habense, Edinger 

 (10, p. 20) ascribes a secretory function, while Rabl-Riickhard 

 (41) homologizes such cells in some amphibia, reptiles and 

 birds with the torus longitudinalis of bony fishes (see Fig. 

 100). In section, the mesencephal is oval with such a slight 

 depression on the dorsimeson (Fig. 25) as hardly to justify call- 

 ing it a sulcus, as does Burckhardt (see p. 261), and except for 

 uniformity the term geminums does not seem applicable. The 

 cavity is oval except at its caudal part (Fig. 26) where it be- 

 comes a mere slit. There is no special lateral expansion at 

 either cephalic or caudal part, and hence no indication, in the 

 adult of lateral recesses. The dorsal union of the geminums 

 is wide, the cinerea occupying the ventral half, with more 

 scattered cells in the alba of the more dorsal portion. These 

 cells extend to the extreme dorsal limit, but only upon a mesal 

 plane (Fig. 25, 26), (.see p. 293). From these cells the 

 cinerea extends on either side in three somewhat illy de- 

 fined concentric layers (Fig. 24-26) as Nakagawa (35) de- 



