MYODOME AND TRIGEMINO-FACIALIS CHAMBER 2738 
which forms part of the actual ventral surface of the brain, 
this lamina being bent at nearly a right angle and presenting 
surfaces that are the one actually ventral and the other an- 
terior. A prootic bridge has not yet begun to be formed, 
but it is shown by Parker (’82) in somewhat older embryos, 
and is there at first separated from the otic portion of the para- 
chordal basal plate by a large fenestra basicranialis posterior 
similar to the one in Amia and Salmo. 
Veit does not give the relations of the internal carotid and 
efferent pseudobranchial arteries to the cartilages bounding 
the fenestra basicranialis of his descriptions, but in small em- 
bryos of this fish (size not given) I found (’09) the internal ca- 
rotid running forward beneath the basis cranii, being there 
joined by the efferent pseudobranchial artery, and the artery 
so formed then turning upward through the fenestra basicrani- 
alis. Whether the part of the fenestra so traversed lies between 
the polar or trabecular cartilages cannot be definitely told by 
comparison with Veit’s figures, but it would seem as if it must 
be between the hind ends of the trabeculae, the membranous 
pituitary sac lying dorsal to the polar cartilages. The con- 
ditions in this fish thus differ from those in the adult Amia only 
in that the efferent pseudobranchial artery does not traverse 
a foramen and canal in the cartilage of the basis cranii before 
falling into the internal carotid, and in that the recti externi have 
not invaded the myodomic space. 
POLYPTERUS 
In the neurocranium of the adult Polypterus there is a large 
pituitary fossa, the posterior portion of which is roofed by a 
horizontal bridge of the so-called sphenoid bone. The hind end 
of the pituitary body projects posteriorly beneath this bridge, 
and Waldschmidt (’87) shows it there surrounded by what he calls 
‘maschiges, fettartiges Gewebe.’ This tissue apparently fills 
the space between the membranous pituitary sac and the walls 
of the cartilaginous pituitary fossa, the space thus correspond- 
ing to the prootic portion of the functional myodome of Amia. 
In his text figure 8, Waldschmidt shows the side wall of the 
