510 ALLIS. [Vov. XII. 
marked angle, or even a slight pointed recessus, directed out- 
ward or outward and backward. The whole diverticulum thus 
seems to correspond to the ventriculus lateralis of Studnicka 
in Petromyzon, with the posterior horn rudimentary, instead of 
wanting, as he states it to be in ganoids and teleosts. The 
lobus in Amia thus seems to correspond internally, as well as 
externally, to the lobus and something more of Petromyzon, 
Dipnoi, and Amphibia, — to the prosencephalon, probably, or to 
part of it, as Gage has suggested (No. 40, p. 297). The origin 
of olfactory nerve fibres at the hind end of the prosencephalon 
in reptiles (Edinger, quoted by Gage, No. 40, p. 262) would 
seem to support this supposition. 
Between the olfactory lobes, and extending downward and 
backward to the commissure cw of Gage (No. 40, p. 282), that 
is, for the full length of the lamina terminalis, there is in the 
bottom of the ventricle of the fore-brain a long and narrow 
median prolongation, directed forward and downward. At the 
upper, anterior end of this median diverticulum there is a slight 
recessus directed forward. in the lamina terminalis at this 
point there is no process properly so called, the recessus being 
apparently formed, as sagittal sections show, by a thinning of 
the substance of the lamina. The lamina here is slightly con- 
vex externally, but less so than in its ventral portion. In trans- 
verse sections the anterior end of the recessus is often cut so 
as to show a slit-like lumen, surrounded or nearly surrounded 
by an egg-shaped layer of cells, the small end of the egg directed 
upward and wedged in between the lobi olfactorii. The process, 
if it can be called such, is the lobus olfactorius impar, and its 
cavity the recessus olfactorius impar of von Kupffer (No. 69), 
or, as it has been later named by Burckhardt (No. 17), the reces- 
sus interolfactorius or recessus neuropricus. 
The nervus olfactorius (o/, Figs. 21, 26, and 64, Pls. XXIV, 
XXV, and XXXVIII) arises from the front end of the lobus, 
and, in the adult, is as long as, or even one half again as long 
as, the brain. It runs directly forward, for fully two thirds of 
its course in the cranial cavity. It then enters the olfactory 
canal (o/c) and, turning slightly outward, issues by the olfactory 
foramen (o/fr, Figs. 8 and 9, Pl. X XI) on the floor of the olfac- 
