218 EDWARD PHELPS ALLIS, JR. 
The foramen faciale perforates the prootic posterior to the 
postorbital process of the neurocranium, the foramen trigem- 
inum perforating the same bone anterior to that process, the 
two foramina both leading directly into the cavum cerebrale 
eranii. Between these two foramina the postorbital process 
of the cranium is perforated by a short canal, the floor of which 
lies at the level of the roof of the myodome and hence dorsal 
to the posterior portion of the floor of the facialis bay. The 
later bay leads directly into this canal, the canal itself leading 
into the orbit and transmitting the vena jugularis, the arteria 
carotis externa, a communicating branch from the nervus fa- 
cialis to the nervus trigeminus, and a sympathetic nerve. This 
canal is thus a jugular canal through the prootic bone, and it 
represents all there is, in this fish, of the trigemino-facialis 
chamber of my description of others of the Teleostei. There 
are in this region of the cranium of fishes three distinctly dif- 
ferent chambers. One is the trigemino-facialis recess of my 
descriptions of the Teleostei and Selachii; another is the jugular 
canal through the prootic, just referred to and which I have here- 
tofore called the teleostean trigemino-facialis chamber; and the 
third is a chamber formed by the fusion of the other two, and is 
the trigemino-facialis chamber of my descriptions of Amia. It is 
accordingly necessary to distinguish between these several cham- 
bers, and the term trigemino-facialis chamber will hereafter be 
limited to the chamber as found in Amia, the two parts of the 
chamber being called its pars ganglionaris and pars jugularis. 
The ventral edges of the side walls of the myodome of Hyo- 
don are nowhere enclosed in perichondrial bone, cartilage always 
projecting ventrally beyond the related bone and abutting 
against dense connective tissue that separates it from the par- 
asphenoid. This tissue is apparently all skeletogenous, for 
there is no definite perichondrial membrane separating it from 
the cartilage. The parasphenoid develops in the outer layers 
of this tissue, and the bases of the diverging hind ends of that 
bone are connected by it across the median line (figs. 8 and 9), 
the tissue there forming a dense and well-defined band-like layer. 
Farther posteriorly this transverse band becomes less dense, 
