~ 
304 EDWARD PHELPS ALLIS, JR. 
two paired cartilages developing as independent pieces in the 
duck, but in the chick in continuity with the anterior edge of 
the parachordal plate. The basal plate is thus completed, and 
it is perforated by a median space, traversed longitudinally 
by the notochord, which is said to be the fenestra basicranialis 
posterior and which has the position of that fenestra in Lacerta 
and the Amphibia. 
The trabeculae appear as independent paired cartilages at 
about the same time as the cartilagines basioticae, lying ros- 
tral to the nervi optici and nearly at right angles to the basal 
plate. An independent cartilago polaris then develops, in the 
duck, on either side of the hypophysis, between the trabeculae 
and the ventral surface of the basal plate, and later fuses with 
both of those cartilages, usually first with the trabeculae, but 
occasionally first with the basal plate. In the chick the carti- 
lago polaris is, from the very first, continuous with the hinder 
end of the trabecula of its side. The fusion of the polar carti- 
lages with the basal plate takes place in the line of the fusion of 
the cartilagines acrochordalis and basioticae, and a fenestra 
hypophyseos is thus enclosed, which lies nearly at a right angle 
to the fenestra basicranialis posterior and is separated from it 
by the cartilago acrochordalis (I. c., p. 426). The side walls of 
this fenestra hypophyseos are at first formed both by the polar 
cartilages and the hinder ends of the trabeculae, but, as the tra- 
beculae gradually fuse with each other in the median line, that 
part of the fenestra which was primarily enclosed between them 
is gradually suppressed, the trabeculae then only forming its 
anterior wall, the tuberculum sellae. The cartilago acrochor- 
dalis, projecting dorso-anteriorly, is said to form the dorsum 
sellae. A processus infrapolaris develops later on either side, 
from the posteroventral surface of the polar cartilage, and in 
Sterna projects posteriorly beneath and parallel to the basal 
plate, its hind end fusing with it on either side of the fenestra 
basicranialis posterior. A somewhat vertical, subparachor- 
dal plate is thus formed which is perforated by a large opening, 
traversed by the arteria carotis interna. That artery, after 
traversing this opening, passes through the fenestra hypo- 
