MYODOME AND TRIGEMINO-FACIALIS CHAMBER Siz 
lateral wall of the pars jugularis of the trigemino-facialis chamber 
is always less extensive than in Amia and may be wholly wanting. 
In Ceratodus there is a trigemino-facialis chamber similar to 
that in Amia, and there is a bar of cartilage which corresponds 
to the pedicel of the alisphenoid of that fish. 
In the Amphibia there is a trigemino-facialis recess, and the 
pars ascendens of the quadrate forms the lateral wall of a space 
corresponding to the pars jugularis of the chamber of the Teleos- 
tei. The ascending process of the palatoquadrate is the homo- 
logue of the pedicel of the alisphenoid of fishes. 
In the Reptilia there apparently is no trigemino-facialis recess, 
the lateral wall of the neurocranium being the primitive cranial 
wall. The pars ascendens of the quadrate forms the lateral 
wall of a trigemino-facialis chamber. The antipterygoid (col- 
umella) is the homologue of the pedicel of the alisphenoid of fishes, 
and the processus basipterygoideus the homologue of the floor 
of the orbital opening of the myodome of Amia. 
In the Mammalia there is a trigemino-facialis recess formed 
by the cava epiptericum and supracochleare. The ala tem- 
poralis is peculiar to mammals; it is a bar of cartilage formed be- 
tween the nervi maxillaris and mandibularis trigemini as they 
issue from the trigemino-facialis recess, the processus alaris cor- 
responding to some part of the side wall of the prespinal portion 
of the myodome of Amia. The ala temporalis has been pro- 
longed anteriorly so as to enclose a space anterior to the tri- 
gemino-facialis recess, and the foramina for the pituitary vein 
(sinus cavernosus) and the nervi oculomotorius, trochlearis and 
profundus (first branch of trigeminus) open into this space and. 
from it into the orbit. The cavum tympanicum is the pars 
jugularis of the trigemino-facialis chamber, and the processus 
pterygoideus, the malleus, incus, and stapes, and probably also 
the annulus tympanicus, are quite certainly portions of the lat- 
eral wall of that part of the chamber. A diverticulum of the 
spiracular canal, or an independent evagination of the pharynx, 
has expanded into this part of the chamber and so formed the 
middle ear. The chorda tympani must then correspond to that 
communicating branch from the nervus facialis to the nervus 
THE JOURNAL OF MORPHOLOGY, VOL. 32, NO. 2 
