MYODOME AND TRIGEMINO-FACIALIS CHAMBER ey 
ascending process of the parasphenoid, and the tissues resulting 
from the resorption of the pedicel of the alisphenoid ossified, in 
certain fishes (Cottus, Gasterosteus), to form an anterior portion 
of that process. i 
The myodomie cavities of the Holostei and Teleostei are rep- 
resented in the Selachii either by canals in the basis cranii which 
are traversed by the pituitary veins and the internal carotid and 
efferent pseudobranchial arteries or by a posterior and deeper 
portion of the large pituitary fossa of the chondrocranium which 
is shut off from the cavum cerebrale cranii by the dura mater, 
and is traversed by the pituitary veins and the internal carotid 
arteries. 
In embryos of Ceratodus there is a subpituitary space, trav- 
ersed by the pituitary veins, which corresponds to the dorsal com- 
partment of the teleostean myodome, and the internal carotid 
canals of Amia have been added tosit. This fusion of these 
canals with the dorsal myodomic cavity is due, either to the 
resorption of the cartilage that separates them in Amia or to a 
shifting posteriorly of both the hypophysis and the internal 
earotids from a position between the hind ends of the trabeculae 
to one between the so-called anterior prolongations of the para- 
chordals. 
In the Amphibia the basis cranii apparently corresponds to 
the roof, and not to the floor, of the dorsal myodomie cavity of 
Amia and the Teleostei. The fenestra hypophyseos of these 
animals is then the homologue of the pituitary opening of the 
brain case of fishes. 
The Reptilia and Mammalia have a dorsal myodomic cavity 
similar to that in Ceratodus. In man it is represented in the 
cavernous and intercavernous sinuses, and the venous vessels 
that traverse the sinuses are the homologues of the pituitary 
veins of fishes. 
The cartilago acrochordalis of Sonies’ and Noordenbos’ de- 
scriptions of birds and mammals, respectively, is the homologue 
of the cartilaginous prootie bridge of embryos of fishes. The 
open space between this cartilage, or bridge, and the anterior 
end of the parachordal plate is the fenestra basicranialis poste- 
