MYODOME AND TRIGEMINO-FACIALIS CHAMBER 261 
region. One of them is the fenestra hypophyseos of Gaupp, 
which lies between the hind ends of the trabeculae and hence 
in the floor of the anterior section of the myodome; and this 
must be, in early embryos, traversed by the internal carotid 
arteries, for Parker (’73) shows those arteries, in this fish, run- 
ning upward anterior to the hypophysis, and I so find them in 
all the Teleostei I have examined. A second fenestra is the 
fenestra basicranialis posterior of Gaupp, which les partly in 
the floor of the middle section of the myodome and partly be- 
tween that section and the posterior section. <A third fenestra, 
not described by Gaupp, lies in the floor of the posterior section 
of the myodome, and this, together with that part of the second 
fenestra that lies .n the floor of the middle section of the myo- 
dome, forms the fenestra ventralis myodomus, the so-called hypo- 
physial fenestra of Sagemehl. The remainder of the second fenes- 
tra—the part leading from the middle section of the myodome 
into the posterior one—is simply a transverse section of the con- 
tinuous cavity of the myodome and does not open on to the 
ventral surface of the cranium. The fourth fenestra lies in 
the roof of the middle section of the myodome, and this alone 
is the homologue of the fenestra basicranialis posterior of the 
Sauropsida. This is evident from Sonies’s (’07) description 
of this fenestra in the chick and duck, to be discussed later, and 
from Gaupp’s (00) account of it in Lacerta. In Lacerta the 
fenestra is said by Gaupp to be bounded anteriorly by the crista 
sellaris, and to be closed by a membrane (Gewebe) everywhere 
continuous with the perichondrium of the bounding cartilages, 
and that represents an unchondrified portion of the primordial 
cranium. The anterior end of the notochord is enclosed in this 
membrane, and lies, in part of its course, so close to its ventral 
surface that it forms a longitudinal ridge along it The fenes- 
tra accordingly les in what corresponds to the roof of the myo- 
dome of fishes, and not to its floor, and hence cannot be the 
homologue of the similarly named fenestra of Gaupp’s descrip- 
tions of Salmo. In the Urodela, also, the fenestra basicranialis 
posterior is said by Gaupp (’05b, p. 692) to be a perforation 
of the basal plate, traversed by the notochord, and lies pos- 
terior to its tip, as it does in Lacerta. 
