MYODOME AND TRIGEMINO-FACIALIS CHAMBER Zao 
sis lies anterior to this ridge, the cross-commissure of the pitui- 
tary veins lying ventral to the hypophysis and separated from 
it by the dura mater. The recti externi have their insertions 
on a median vertical membrane, immediately posterior to the 
pituitary veins and immediately anterior to the summit of the 
transverse ridge. They are surrounded by connective tissue 
that resembles the fatty tissue found abundantly in this fish, 
but are not otherwise separated from the other rectus muscles, 
the dorsal and ventral myodomic compartments thus appa- 
rently here being confluent. 
SALMONIDAE 
In Salmo, Parker (’73) and Stohr (’82) found the trabeculae 
and parachordals primarily independent of each other. Stohr 
also found the anterior portions of the parachordals—the parts 
corresponding to the anterior prolongations of the parachordals 
of Swinnerton’s descriptions of Gasterosteus—primarily inde- 
pendent of the posterior portions, and he considered them to 
represent the ‘Balkenplatten’ of the Amphibia. They are 
said by him to fuse, first, with the posterior portions of the para- 
chordals and then with the trabeculae. Of the adult Salmo, 
Parker’ says (i"c., ‘p. 102): 
One remarkable change in the investing mass, as a whole, is the 
growth downward of a lamella on each side, thus forming a covered 
archway; for in front of the retiring notochord the moieties of cartilage 
meet, and this viaduct is floored by the submucous bone which has 
been removed, the parasphenoid. All the true axial parts of the skull 
cease at the front edge of the investing mass behind the pituitary space; 
all the rest has a facial foundation, is built on the trabeculae, or has a 
secondary character as a development of the cranial wall. 
This so-called covered archway is the myodome, which is thus 
considered by Parker to be bounded laterally by downgrowths 
of the parachordal cartilage and not by those cartilages, them- 
selves, bent down. 
Schleip says (’04, pp. 355 to 359) shied in trout embryos, 
12 to 14-mm. in length, the parachordals ae trabeculae form 
the floor of the primordial cranium, and that the cartilages of 
