140 Cincinnati Society of Natural Histo?y. 



from the taenia thalami enter the corpus geniculatum. The super- 

 ficial and tortuous path of the tract makes it hard to follow. 

 (Compare Plate VIII. , Figs. 10-16 ; Plate IX., Figs. 6, 8,9 ; Plate 

 XV., Figs. 4, 5 an( 3 7)- 



Osborn {Jour. Morph., Vol. 1.) describes this bundle as follows: 

 " It divides into two distinct bundles, one of which descends into 

 the inner mantle of the hemispheres, and finally disappears, after 

 bending around the inner portion of the mantle. The second bun- 

 dle descends directly along the outer wall of the thalami. One fact 

 militates against our considering the commissures as a purely decus- 

 sational system; that is, the bundle entering the hemispheres is 

 larger than that entering the thalami.'' In the alligator a number 

 of fibres leave the bundle as it is about to pass into the hemi- 

 spheres turning backward, but their further course was not traced. 

 Comp. Ahlborn (" Untersuch. u. d. Gehirn d. Petromyzonten," 

 p. 285). 



(Y) Meynerfs bundle is a bundle extending from the region below 

 the superior commissure, and passing obliquely backward and ven- 

 trad near the median line, to an indistinct ganglionic mass near the 

 exit of the third nerve. It would appear that this ganglion corre- 

 sponds to the ganglion interpedunculare of authors (Plate IX , 

 Fig. 9)- 



(/.) The ascending fibres of the inferior commissure lie parallel 

 to those of the tractus opticus for some distance, but their further 

 course was not traced. 



{£). The posterior commissure is well seen in transverse sections. 

 In longitudinal sections a strong bundle of fibres springing from 

 the region of the commissure passes ventrad to unite with 

 ascending peduncular tracts, with which it passes apparently toward 

 the cerebrum. Much remains to be done in this portion of the 

 brain. 



(/*.) The median commissure, as elsewhere shown, is but an adhe- 

 sion of the walls of the third ventricle at the bifurcation, with few 

 fibrous connections. 



2. Microscopic structure of olfactory lobes. The same structure is 

 observed in the olfactory bulb as in other vertebrates, and only a 

 few slight modifications need be mentioned. Sections through the 

 olfactory bulb display an outer fibre-zone passing into the tortuous 

 glomerular layer, which is separated by a homogeneous or gelatin- 

 ous layer from that containing the ganglion cells. The irregular, 



