MYODOME AND TRIGEMINO-FACIALIS CHAMBER DET 
and it is unusually large in both these specimens. It there- 
fore seems certain that, if Parker’s figures and descriptions be 
not wholly wrong in this particular respect, the specimen ex- 
mined by him must have been exceptional and abnormal. 
In my work on Mustelus (’01), I found the canalis trans- 
versus of Gegenbaur’s descriptions traversed by the pituitary 
veins, and not by a lymph vessel, and this was later confirmed 
by work on other Selachii (Allis, ’14 a). In this latter work I 
found the deeper, posterior portion of Gegenbaur’s descriptions 
of the pituitary fossa particularly well developed in Chlamy- 
doselachus, and I said of it that it had ‘‘the appearance of 
being a somewhat separate and independent fossa.’ It is sub- 
pituitary, as well as subdural in position, and is filled with tissues 
that seem to be in part tough connective tissues and in part 
of a different character. 
In all the Selachii I have examined or can find described, 
the internal carotid arteries always le anteroventral to the pitui- 
tary veins, as they do in the Teleostei and Holostei, and they are 
always separated from those veins by either membrane or carti- 
lage. They always either fuse with each other in the median 
line, or are there connected by cross-commissure, and this fusion 
of the arteries is certainly not due, as it apparently is in the 
Teleostei, to any pressure of the muscles of the eyeball. In 
Heptanchus, Mustelus, and Acanthias I found these arteries 
joined by the efferent pseudobranchial arteries, either while 
still in the cartilage of the basis cranii or while lying between 
that cartilage and the lining membrane of the cavum cerebrale 
cranil. The internal carotids of these fishes thus do not enter the 
cavum cerebrale cranii until after they have received the efferent 
pseudobranchial arteries, which perforate the side walls of 
the pituitary fossa slightly anterior to the internal carotid 
canals, approximately in the region between the hind ends of 
the lobi inferiores and the pituitary body. In Chlamydose- 
lachus I found the internal carotids entering the cavum cerebrale 
cranii before they received the efferent pseudobranchial arteries, 
but I now think this may be an error. The nervus palatinus 
facialis does not, in any of these fishes, come into any relation 
