278 EDWARD PHELPS ALLIS, JR. 
to any part of the pituitary fossa, running forward, after issu- 
ing from the cranial cavity, ventral to the chondrocranium. 
The early development of the cartilages in this region of 
these fishes differs somewhat from that in the Teleostei and 
Holostei. According to Sewertzoff (99), the trabeculae, when 
first formed, are independent cartilages, which lhe oral, and 
hence morphologically ventral, to the hypophysis, and because 
of the marked cranial flexure at this stage of development, 
these cartilages lie ventral to the parachordal plate and per- 
pendicular to it, slightly posterior to its anterior edge. In 
later stages of development the anterior portions of the tra- 
beculae are said by him to fuse with each other, their hind ends 
still remaining separate, but having now fused with the ventral 
surface of the parachordal plate. An opening is thus enclosed 
between the trabeculae and the parachordal plate, and the 
hypophysis is said to traverse it. It is called by Sewertzoff the 
intertrabecular basal fontanelle, and, as shown by Parker in 
Seyllium (’76, fig. 6, pl. 35), has approximately the extent of 
the pituitary fossa of the adult fish. In later stages this large 
fontanelle is greatly reduced by progressive fusion of the tra- 
beculae, both anterior (ventral) and posterior (dorsal) to the 
hypophysis, but Sewertzoff says that the hypophysis still pro- 
jects through it, and he so shows it in transverse sections of 
embryos of Acanthias (I. c., figs. 14 and 15, pl. 30). The stalk 
of the hypophysis is said to run forward from this point and to 
end blindly, and it apparently does not traverse the persisting 
portion of the basal fontanelle in Acanthias, but it does in Pris- 
tiurus (I. c., figs: 23 to 25, pl. 31). 
The course of the internal carotid and efferent pseudo- 
branchial arteries is not given by Sewertzoff, but the internal 
carotids must certainly have traversed the posterior portion 
of the large primitive fontanelle, and hence that part of that 
fontanelle which persists in the oldest embryos of Acanthias 
described by him. It would, however, seem as if they could 
not have traversed that part of the fontanelle that persists in 
Pristiurus, for that part lies considerably anterior to the hy- 
pophysis, between the hind edges of the fenestrae opticae (I. c., 
