306 EDWARD PHELPS ALLIS, JR. 
tra hypophyseos of embryos of fishes has been suppressed in 
advanced embryos of the chick and duck. 
In Talpa, Noordenbos (’05) finds the parachordals of oppo- 
site sides, when first developed, united with each other, ventral 
to the notochord, and not extending to its tip. The tip of the 
notochord reaches, at this stage, to the hypophysis, and is said 
to represent, in a certain sense, the morphological anterior end, 
or anterior pole, of the embryo, the hypophysis being an organ 
at that pole. In slightly older embryos the notochord is some- 
what withdrawn from the hypophysis, and its tip then doubt- 
less lies posterior to the infundibulum. The parachordal plate 
has at the same time grown rostralward, and, turning upward 
at its anterior end, now surrounds the notochord, which tray- 
erses it from its dorsal to its ventral surface and extends 
anteriorly beyond it. 
The trabeculae first appear as a single median plate between 
the nasal sacs and extending posteriorly to the recessus preop- 
ticus. In the space between the trabecular and parachordal 
plates, ventral to the hypophysis and at a slightly lower level 
than the parachordal plate, two pairs of little cartilages, the 
insulae polares, later appear, and soon fuse to form a polar plate 
which is at first perforated by a median fenestra hypophyseos, 
which soon becomes closed by growth of the bounding cartilage. 
This polar plate fuses, soon after its formation, with the tra- 
becular plate, and in the line of fusion a slight transverse fur- 
row is formed which lodges the chiasma opticum. The hind 
edge of this furrow is slightly raised, and forms the tuberculum 
sellae, which thus lies on the anterior end of the polar plate and 
not, as in the chick and duck, on the hind ends of the trabec- 
ulae. No cartilago acrochordalis has yet been formed, and the 
polar plate accordingly cannot fuse with the basal plate along 
the line of fusion of that cartilage with the cartilagines basi- 
oticae, as it does in the chick and duck. Accordingly, a direct 
fusion of the polar plate with the basal plate does not take 
place, and connection with the latter plate is acquired through 
the intermediation of a delicate Y-shaped mass of cartilage, the 
arms of which fuse with the projecting anterior ends of the 
