MYODOME AND TRIGEMINO-FACIALIS CHAMBER 259 
from the side wall of the cranium, extending posteriorly dorsal 
to the notochord, and anteriorly passing into the supraseptal 
membranous floor of the cavum cerebrale cranii in the orbito- 
temporal region. In this membranous roof of this middle sec- 
tion of the myodome a transverse bridge of cartilage, the prootic 
bridge, is later developed, and it is said to lie above and anterior 
to the tip of the notochord. In the adult this bridge extends 
forward to the hind edge of the hypophysis, as shown in Parker’s 
figure of a bisected skull (’73, fig. 4, pl. 7), and the pituitary 
opening of the brain case lies considerably posterior to the an- 
terior edges of the ventral processes of the prootics. It must 
then be that, as in the adult Gasterosteus, the hypophysis of 
the adult Salmo lies dorsal to the interparachordal fenestra and 
not dorsal to the fenestra hypophyseos. 
The middle section of Gaupp’s descriptions of the myodome 
thus apparently corresponds to the subpituitary portion of the 
prespinal section, and to all of the prootic portion of the spinal 
section, of my descriptions. Gaupp says that, primarily, the 
nervus palatinus facialis issues from the cranial cavity along 
the lateral edge of the anterior parachordal, but that, as the 
myodome gains in height and breadth, the nerve becomes in- 
cluded in it, then entering it by perforating its membranous 
roof and leaving it through a foramen in its floor. The course 
of the internal carotid arteries is not given, but as there are no 
special perforations of the basis cranii for them, they must pass 
upward through the fenestra hypophyseos. Gaupp_ shows, 
in his figure of the entire chodrocranium, a foramen lying be- 
tween the foramen for the nervus facialis and the incisura pro- 
otica, and it is said to give passage to the vena jugularis, coming 
from the anterior portion of the cranial cavity. This vein is, 
however, certainly not the jugularis of current descriptions of 
fishes, and is probably the encephalic vein of Allen’s (’05) de- 
scription of the Loricati. It cannot be the pituitary vein, 
for that vein does not extend into the anterior portion of the 
cranial cavity. 
The posterior section of the myodome is said to lie beneath 
the basis cranii, between it and the parasphenoid, and to com- 
