ZOOLOGY: E. P. ALUS 
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sphenoid. In the latter case the nerves, arteries, veins and muscles all have 
the same relations to this process that they have to the pedicel of the alisphe- 
noid of Amia. The 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 that 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 that corresponds to the pars 
jugularis of the chamber of the Teleostei. The ascending process of the 
palatoquadrate is the homologue 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 (columella) 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 temporalis is peculiar to mammals, 
and is a bar of cartilage formed between the nervi maxillaris and mandibularis 
trigemini as they issue from the trigemino-facialis recess, the processus alaris 
corresponding to some part of the side wall of the prespinal portion of the myo- 
dome of Amia. The ala temporalis has been prolonged anteriorly so as to en-, 
close a space that lies anterior to the trigemino-facialis recess, and the foras 
mina for the pituitary vein (sinus cavernous) and the nervi oculomotorius, 
trochlearis and profundus (first branch of trigeminus) open into this apace 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 possibly also the annulus tympariicus, are quite certainly por- 
tions of the lateral 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 ner- 
vus facialis to the nervus trigeminus that, in fishes, traverses the trigemino- 
facialis chamber, and hence must be a prespiracular nerve. 
The internal carotid artery enters the crania 1 cavity, in most vertebrates, 
by passing upward mesial to the related trabecula, or mesial to that posterior 
prolongation of the trabecula that is formed by the polar cartilage, but in 
Ameiurus it enters the cranial cavity through the foramen opticum, and hence 
would seem there to pass lateral and then dorsal to the trabecula. In em- 
bryos of the Mammalia ditremata also this artery is said to pass upward lat- 
eral to the trabecula, but it is probable that it here simply passes lateral to 
