290 EDWARD PHELPS ALLIS, JR. 
wall of the pars jugularis of this chamber of fishes, and the 
pedicel of the alisphenoid are represented, respectively, in the 
Amphibia by the otic and ascending processes of the quad- 
rate, the latter process being the homologue of the antiptery- 
goid of the Reptilia (Allis, 714 c). These two portions of the 
neurocranium of fishes are thus secondarily acquired additions 
to it, and one or the other, or even both of them, is frequently 
wanting. In the Selachii, the pars ganglionaris of the tri- 
gemino-facialis chamber may be separated, by a partition of mem- 
brane or cartilage, into trigeminus and facialis portions, the 
latter portion then fusing with an acusticus recess to form an 
acustico-facialis recess. 
Assume that, in a piscine skull, the pedicel of the alisphenoid 
and the lateral wall of the pars jugularis of the trigemino-faci- 
alis chamber are both wanting, as is actually the case in certain 
of the Teleostei; that independent trigeminus and acustico- 
facialis recesses have been formed, as in certain of the Selachii; 
that the muscles of the eyeballs have not acquired entrance into 
the preexisting myodomie cavities, as in many fishes; that these 
cavities have been reduced to the conditions found in Cerato- 
dus; and that the trigeminus recess has been enlarged to such 
an extent that its floor projects ventrally below the level of the 
pituitary fossa (sella turcica), as it actually does in many of the 
Mammalia. If the wall separating the trigeminus and acusti- 
co-facialis recesses were then to be perforated, the facialis por- 
tion of the latter would be in communication with the trigemi- 
nus recess, and conditions would arise similar to those described 
by Voit (09) in rabbit embryos, where the cavum epiptericum 
(trigeminus recess) and the cavum supracochleare (facialis 
recess) form a continuous cavity which communicates with the 
meatus acusticus internus (acusticus recess) through a foramen 
faciale primitivum. The facialis nerve would then issue from 
the facialis portion of this continuous cavity through a foramen 
faciale secundarium, the profundus nerve (first branch of the 
trigeminus) and trigeminus issuing from the trigeminus portion 
of the cavity, and their foramina of exit lying at the hind end 
of the orbit and not far from the foramina of the pituitary vein 
