MYODOME AND TRIGEMINO-FACIALIS CHAMBER 305 
physeos, posterior to the hypophysis, sends a cross-commissural 
branch to its fellow of the opposite side, another branch, the 
arteria opthalmica interna, outward dorso-anterior to the polar 
cartilage, and is then itself distributed to the brain. It passes 
mesial to the polar cartilage of its side, but lateral and dorsal 
to the processus infrapolaris. If this latter process were to be- 
come the only connection between the polar cartilage and the 
basal plate, the artery would pass lateral to the polar cartilage, 
and this is apparently what actually takes place in the Mam- 
malia, as will be explained later. 
Comparing these conditions in the chick and duck with those 
in embryos of the Teleostei and Holostei, it is at once evident 
that the cartilago acrochordalis of the former must be the homo- 
logue of that cartilaginous prootic bridge of the latter which 
forms the beginning of the definitive prootic bridge. The re- 
lations of these two cartilages to the other skeletal elements, 
and to the brain, are too strictly similar to leave any reasonable 
doubt as to this, the differing relations of the cartilages to the 
notochord evidently being related to the early development of 
the cartilage in the chick and duck and its late development in 
the Teleostei and Holostei. The space which, in the Teleostei 
and Holostei, lies between this bridge and the otic portion of the 
basal plate must then be the homologue of the fenestra basi- 
cranialis posterior of the chick and duck, as has already been 
stated, and the side walls of this fenestra the homologues of 
the basiotic cartilages; these latter cartilages being prolonged 
ventrally, in fishes, by the ventral processes of the prootics, 
and, in the chick and duck, by the infrapolar processes. These 
latter processes, together with the polar cartilages, are then the 
so-called anterior prolongations of the parachordals of Swinner- 
ton’s and Gaupp’s descriptions of Gasterosteus and Salmo, there 
apparently developed in continuity with the basiotic cartilages, 
as they are said to be in certain of the Aves. The so-called 
fenestra basicranialis posterior, or fenetra interparachordalis, 
of Gaupp’s and Swinnerton’s descriptions of fishes is then the 
homologue of the fenestra hypophyseos of the chick and duck 
and not of the fenestra basicranialis posterior, and the fenes- 
