MYODOME AND TRIGEMINO-FACIALIS CHAMBER 291 
and the oculomotorius, trochlearis, and abducens nerves. In 
the Teleostei and Selachii these several last mentioned fora- 
mina may lie relatively close together, and the chondrification 
or ossification of the tissues of the cranial wall may actually give 
rise to marked variations in the number and arrangement of 
the definitive foramina. Assume that the tissues surround- 
ing the nervi maxillaris and mandibularis trigemini, as they 
issue from the trigeminus recess, chondrify to form a vertical 
bar of cartilage; that this bar grows forward so as to shut in 
the other foramina mentioned above, as the pedicel of the ali- 
sphenoid actually does in Amia; and that the tissues separating 
these other foramina from each other and from the nervus 
maxillaris persist as membrane. This would give rise, in this 
hypothetical cranium, to three fenestrations of the cranial wall 
which would be strictly similar, so far as the nerves travers- 
ing them are concerned, to the fissura orbitalis superior and the 
foramina ovale and faciale secundarium of Voit’s description 
of embryos of the rabbit. If, then, the venous and arterial 
vessels of the region also have the same relations to these fora- 
mina that they do to the foramina in the rabbit, there would 
seem to be no reasonable doubt that the foramina, and hence 
their bounding walls, are strictly homologous. 
In fishes the vena jugularis always runs posteriorly mesial to 
the pedicel of the alisphenoid, when the pedicel exists, and then 
always traverses the pars jugularis of the trigemino-facialis 
chamber, when it is present and independent of the pars gan- 
ghonaris. When the pars jugularis of the chamber is wanting, the 
vein passes along the lateral wall of the neurocranium, whether 
that wall be formed by the primary wall of the cranial cavity or 
by the lateral wall of a trigemino-facialis recess, never enter- 
ing either the recess or the cavum cerebrale cranii. The pit- 
uitary vein arises from this vena jugularis and perforates the 
cranial wall, anterior to the trigemino-facialis chamber, to enter 
the dorsal myodomic cavity, never itself entering either the ca- 
vum cerebrale cranii or any part of the trigemino-facialis cham- 
ber. A branch is, however, sent into the cavum cerebrale cranii. 
to drain the hypophysis, and, in certain Teleostei, this branch 
