MYODOME AND TRIGEMINO-FACIALIS CHAMBER 307 
parachordal plate. This Y-shaped cartilage, probably together 
with the posterior pair of insulae polares, thus corresponds to 
the infrapolar processes of the chick and duck, and the internal 
carotid arteries run upward lateral to them, as they do in the 
chick and duck and as explained just above. 
The Y-shaped cartilage of Talpa, by its fusion with the 
anterior end of the parachordal plate, encloses a circular open- 
ing which Noordenbos calls the fenestra basicranialis posterior. 
The anterior end of the notochord les directly above this fenes- 
tra, which it would not do were the fenestra the homologue of 
the similarly named fenestra in the chick and duck. Further- 
more, Noordenbos says (’05, p. 385) that the hypophysis lies 
in a slight fossa, bounded anteriorly by the tuberculum sellae 
(a ridge formed, as above stated, on the anterior end of the polar 
plate) and posteriorly by the anterior end of the parachordal 
plate, thus necessarily lying directly above the so-called fenes-. 
tra basicranialis posterior, instead of, as in the chick and duck, 
definitely anterior to it. This fenestra of Talpa must then be 
ah opening corresponding to some part of Gaupp’s fenestra 
basicranialis posterior of Salmo, and apparently to that part 
of it which he says leads from the middle into the posterior 
sections of his descriptions of the myodome. The fenestra of 
Talpa is, in any event, not a perforation of the floor of the cavum 
cerebrale cranii, as it is in the chick and duck, and that per- 
foration, and a cartilago acrochordalis are both wanting in these 
embryos. The dorsum sellae of these early embryos is then 
not the homologue of the posteclinoid wall of Amia and the Tel- 
eostei, nor of the dorsum sellae of Sonies’s descriptions of the 
chick and duck. It is, however, possible that a cartilago acro- 
chordalis may be developed in later stages than those described 
by Noordenbos, for Voit shows this cartilage in his figures of 
embryos of the rabbit, there perforated by an opening, the evi- 
dent homologue of the fenestra basicranialis posterior of Sonies’s 
descriptions of the chick and duck; and Faweett (’10), in a work 
I have not been able to consult, is said by Kernan (16, p. 621) 
to have found the dorsum sellae separated from the crista trans- 
versa in 19-mm. and 21-mm. human embryos, the dorsum sellae 
