MYODOME AND TRIGEMINO-FACIALIS CHAMBER 295 
and no suppositions have been made in regard to the latter that 
are not warranted by conditions actually found in fishes, ex- 
cepting only the formation of a bar of cartilage between the 
nervi maxillaris and mandibularis trigemini and the fusion of 
the foramen for the nervus maxillaris with certain other foramina 
to form a single large fenestra; and, as already stated, marked 
variations in the fusions and groupings of the foramina in this 
region are of constant occurrence in fishes. It thus seems cer- 
tain that the foramina in this region in the two crania are homol- 
ogous, and it follows that the lamina ascendens of the ala tem- 
poralis of mammals is a bar of cartilage formed between the nervi 
maxillaris and mandibularis trigemini as they issue from a 
trigemino-facialis recess, and this element of the cranium is 
apparently characteristic of these vertebrates. The processus 
alaris of the ala temporalis must then be represented in some 
ventral portion of the basicapsular commissures of fishes, and 
apparently in that part which, in Amia, lies between the 
palatine foramen and the floor of the orbital opening of the 
myodome. If it includes the latter floor, it must include the pro- 
cessus basipterygoideus of reptiles, which seems improbable. 
Certain other features of the region, which favor this inter- 
pretation of the conditions, may now be considered. 
The myodomic cavity of the mammalian cranium, corre- 
sponding to the so-called cavernous and intercavernous sinuses 
of man, must necessarily extend, on either side, beyond the 
lateral edge of the foramen caroticum, and its roof is thus formed 
by what Terry (17) has recently described as the spreading 
basal portion of his membrana limitans. The carotid foramen 
accordingly hes in the floor of this myodomic cavity and not, 
as Voit (09) concluded was the case in rabbit embryos, in the 
floor of the cavum epiptericum. The nervus petrosus super- 
ficialis major (nervus palatinus facialis) of the rabbit does, how- 
ever, perforate the floor of the cavum epiptericum, as Voit con- 
cluded, this being in accord with its course in the Teleostel, 
where it usually perforates the floor of the pars ganglionaris of 
the trigemino-facialis chamber, but may occasionally perforate 
the floor of the pars jugularis. 
