246 
probable one than the possible one that I have above suggested from 
the basal portion of the selachian eyestalk, than that suggested by 
Veit from the subocular shelf alone of those same fishes, or than 
that suggested by Gaupp (1906) of a special outgrowth of the carti- 
lage of the basis crani developed in relation to the processus basalis 
of his nomenclature. 
The trigemino-facialis recess of Scomber and Scorpaena is the 
homologue of the trigemino-facialis portion of the acustico-trigemino- 
facialis recess of Chlamydoselachus, and the trigemino-facialis chamber 
of the former fishes is the homologue of the chamber that would arise 
by the fusion of the internal jugular, external carotid, trigeminus and 
facialis canals, and the basal portion of the palatinus facialis canal, 
of Acanthias. Whether it is also the homologue of the correspon- 
dingly named chamber of Lepidosteus depends upon whether the 
trigemino-facialis recess of Scomber and Scorpaena is or is not in- 
cluded in the chamber of Lepidosteus. 
In Cottus and Argyropelecus the trigemino-facialis recess is 
found but the trigemino-facialis chamber is apparently wanting 
(Aruıs, 1909), the middle one only of the three walls potentially 
present in this region here having undergone chondrification and 
subsequent ossification. 
In Amia quite different conditions exist from those found in 
any of the fishes above described, and they approach much more 
closely the conditions found in man. In Amia the pituitary fossa 
and the pituitary canal, already found fused in teleosts, Lepidosteus 
and certain selachians, have fused also with the trigemino-facialis 
chamber, and to the chamber so formed a space has been added that 
is extracranial in all of those other fishes. This extracranial space 
in represented by the space that lies between the basisphenoid and 
parasphenoid legs of the alisphenoid bone of Amia, and it has been 
added to the cranial cavity of Amia either by the incorporation in 
the neurocranium of that fish of the selachian eyestalk, as I have 
recently suggested (Allis, 1914), or by the chondrification of an 
anterior extension of the membranous tissues that give origin to the 
outer wall of the teleostean trigemino-facialis chamber. The larger 
part of the trigemino-facialis chamber of Amia lies, as in Lepidosteus 
and teleosts, anterior to the prootic bridge. The inner wall of the 
chamber is membranous, and as the trigemino-facialis ganglionic com- 
plex les wholly external to this membrane, this wall of the chamber 
