MYODOME AND TRIGEMINO-FACIALIS CHAMBER 289 
fishes, and in Amia it enters the orbital opening of the myodome 
and then traverses the trigemino-facialis chamber, lying always 
external to the wall of the cavum cerebrale craniil. Gaupp con- 
siders this vein to be the homologue of the sinus cavernosus of 
mammals, and as that sinus is intracranial in position, he con- 
cludes that the space traversed by the vein in Lacerta, which 
is actually extracranial, has been added to the cranial cavity in 
mammals. The sinus cavernosus is, however, a branch of the 
vena cardinalis anterior (capitis media), and not that vein 
itself, as will be later explained. 
MAMMALIA 
Properly to explain the conditions in mammals it is necessary 
first to consider the ala temporalis. This element of the cra- 
nial wall has been considered by many authors to have its homo- 
logue in the antipterygoid of reptiles, but Gaupp considers it, as 
stated above, the homologue of the processus basipterygoideus 
of those vertebrates. A well-recognized objection to its being 
the homologue of the antipterygoid of the Reptilia is that 
the nervus maxillaris trigemini (second branch of the trigemi- 
nus) les posterior to that element of the reptilian cranium, but 
anterior to the ala temporalis of mammals. Gaupp accounts 
for this by saying that, because of the absence of an antiptery- 
goid in mammals, there was no intervening skeletal element, 
and the nerve has simply joined the first branch of the trigem1- 
nus instead of remaining with the third. Other authors have 
suggested that the nerve has either cut through or slipped over 
the top of the antipterygoid, or simply, for some unknown rea- 
son, chosen a presumably more direct or advantageous course 
on the other side of it. My work leads me to quite a different 
conclusion, and I look for the homologue of the ala temporalis 
in a part of the lateral wall of the trigemino-facialis recess of 
fishes. 
In all of the lower vertebrates there is apparently always either 
a trigemino-facialis chamber, a pars ganglionaris of that chamber 
(trigemino-facialis recess), or both partes ganglionaris and jugu- 
laris separated from each other by a wall of bone. The outer 
