MYODOME AND TRIGEMINO-FACIALIS CHAMBER 285 
The internal carotid artery of Rana is said by Gaupp (’93 b), 
p. 403) to pass upward, in early embryos, mesial to the trabe- 
cula of its side, but, because of enveloping growth of the trabe- 
cular cartilage, soon to become enclosed in a primary foramen 
caroticum. Having traversed this foramen and entered the 
cranial cavity, the artery gives off the arteria carotis cerebralis- 
and then itself issues from the cranial cavity through the foramen 
oculomotorium as the arteria ophthalmica. In later stages, 
that part of the trabecula between the foramina caroticum and 
oculomotorium is resorbed, and the internal carotid is said then 
to lie in the orbit and to send its cerebral branch inward through 
the foramen oculomotorium. Comparing these conditions in 
Rana with those I have described in the Teleostei, it is evident 
that the primary foramen caroticum of Rana must he in what 
corresponds to the floor of the cavum cerebrale cranii of Amia 
and the Teleostei, for that floor, alone, is continuous with that 
part of the cranial wall which is perforated by the foramen 
oculomotorium. 
The nervus abducens of Rana is said by Gaupp to issue from 
the cranial cavity in the sheath of the ramus orbitonasalis tri- 
gemini, and to pass, with that nerve, under, and hence morpho- 
logically anterior to, the processus ascendens quadrati. In fishes 
the corresponding branch of the trigeminus (nervus profundus) 
passes mesial and anterior to the pedicel of the alisphenoid, 
and always lies dorsolateral to the myodome, never traversing 
it. Comparison of these conditions would accordingly indi- 
cate that the dorsal myodomic cavity is wanting. in Rana. In 
Salamandra, Fuchs (10) shows the nervus abducens perforat- 
ing the basis cranii and then lying mesial to the arteria carotis 
interna in a canal between the basis cranii and the parasphenoid, 
the nervus palatinus facialis lying lateral to the carotis interna. 
The hypophysis lies in a perforation of the basis eranii, and 
even projects ventrally slightly beyond it, lying in a slight con- 
cavity on the dorsal surface of the parasphenoid. The dorsal 
myodomic cavity must accordingly be wholly suppressed here 
by failure of the ventral processes of the prootics to develop, 
the canal which lodges the internal carotid artery and the nervus 
JOURNAL OF MORPHOLOGY, VOL. 32, No. 2 
