MYODOME AND TRIGEMINO-FACIALIS CHAMBER Dok 
adults of these fishes I described a well-developed trigemino- 
facialis recess. In embryos this recess is not evident, but it 
must necessarily exist, potentially. 
SYNGNATHUS ACUS 
In a 115-mm. specimen of this fish the myodome and the fen- 
estra ventralis myodomus are both limited to the prootic re- 
gion. Posterior to the hind end of this fenestra is a shallow 
median groove on the ventral surface of the cartilaginous basis 
eranii, which extends into the basioccipital region and there 
lodges the hind end of the parasphenoid. This bone is tri- 
angular there, in transverse section, the apex of the triangle 
directed dorsally. In sections passing through the posterior 
portion of the fenestra ventralis myodomus, the parasphenoid 
is still triangular, and the cartilage bounding the fenestra on 
either side becomes entirely enclosed in perichondrial bone 
which forms part of the prootic. The parasphenoid lies directly 
between the ventromesial edges of these prootic bones, dense 
connective tissue filling the space between the parasphenoid 
and either prootic and also extending dorsally across the para- 
sphenoid, there filling and closing the fenestra ventralis myo- 
domus. Proceeding anteriorly in the sections, the parasphe- 
noid becomes flatter and wider, and the cartilage in the ventral 
ends of the prootics vanishes. Further forward in the sections, 
a little space appears in the dense connective tissue that covers 
the dorsal surface of the parasphenoid, and in this space the 
hind ends of the recti externi soon appear (fig. 23), lying directly 
above the parasphenoid and separated from the cavum cere- 
brale cranii by membrane which continues the full length of 
the myodome and represents the prootic bridge. 
Proceeding forward from this point, the parasphenoid begins 
to widen and at the same time to thicken dorsoventrally, and 
it soon has, in sections, a median circular portion with laterally 
projecting flanges, each flange being formed of external and 
internal plates which receive the ventral end of the ventral 
process of the prootic between them (fig. 22). In the rounded 
median portion of the bone a median cavity forms, and lodges 
JOURNAL OF MORPHOLOGY, VOL. 32, NO. 2 
