284 EDWARD PHELPS ALLIS, JR. 
other and become part of the pituitary fossa of the chondro- 
cranium. Whether this part of the fossa is separated from the 
cavum cerebrale cranii by the dura mater or not cannot be told 
from my specimen, but comparison with other fishes and with 
higher vertebrates show that it must be. 
There are thus, certainly, in this fish, both dorsal and ven- 
tral myodomic cavities, and the dorsal cavity has apparently 
fused with the prepituitary portions of the canals traversed by 
the internal carotid arteries to form a single peripituitary space 
similar to that found in higher vertebrates and represented in 
the cavernous and intercavernous sinuses of man, as will be 
explained later. The foramina carotica lie at the hind edge of 
the pituitary fossa, as they do in higher vertebrates. The cross- 
commissure connecting the internal carotids is evidently the 
homologue of the cross-commissure in the Selachii, and probably 
not the homologue of the anastomosis of the arteries of opposite 
sides in the Teleostei. 
The bar of cartilage separating the foramina sphenoidea 
majus and minus is the homologue of the pedicel of the alisphenoid 
of Amia, and if the anterior edge of this bar of cartilage were 
to grow forward so as to pass beyond the foramina for the pit- 
uitary vein and the oculomotorius and trochlearis nerves, it 
would give rise to the orbital opening of the myodome of Amia. 
AMPHIBIA 
In the Amphibia there apparently is no vein comparable to 
the pituitary vein of fishes, for I find no such vein described, 
and the pituitary region is said to be drained, in certain of these 
vertebrates, by branches of intracranial veins. It might be 
assumed that the myodomic conditions here were as in Amiu- 
rus, where the pituitary veins are also wanting, but it seems 
much more probable that the ventral processes of the prootics 
have here been wholly suppressed, and that the basis cranii 
corresponds to the roof of the dorsal compartment of the myo- 
dome of fishes, and hence represents the primary basis cranii. 
The course of the internal carotid artery in Rana, and that of 
the nervus abducens both in Rana and Salamandra, favor this 
interpretation. 
