276 EDWARD PHELPS ALLIS, JR. 
PLAGIOSTOMI 
Gegenbaur (’72) describes, in the Selachii, a large pituitary 
fossa (Sattelgrube), which extends from the postclinoid wall 
(Satellehne) to a traverse presphenoid bolster (Praesphenoid- 
vorsprung) which lies slightly anterior to the foramina optica, 
and is said to lodge the lobi inferiores anteriorly and the pitui- 
tary body posteriorly. The presphenoid bolster is said to vary 
greatly in importance in different species of the Selachii and 
to be wholly wanting in some of them, the Scylliidae being in- 
cluded among the latter. The pituitary fossa is, in certain of 
these fishes, everywhere lined with the dura mater, this mem- 
brane forming both the perichondrial lining of the fossa and 
the sae which encloses the pituitary body. In others of these 
fishes there is a deeper, posterior portion of the fossa, shut off 
from the cavum cerebrale cranii by a portion of the dura mater 
which extends dorsoposteriorly from its anterior edge to the 
summit of the postclinoid wall. This subdural portion of the 
fossa is said to be traversed by the arteria carotis interna (vor- 
dere Carotis), by a vein, and by a lymph canal which Gegen- 
baur calls the canalis transversus. When this subdural space 
is wanting, the canalis transversus and the internal carotid ar- 
teries are separately enclosed in the cartilage of the basis cranil. 
Parker (’76) later described the conditions in Scyllium canic- 
ula, and in his figures of embryos of that fish he shows condi- 
tions in the pituitary region strictly similar to those described 
and figured by Gegenbaur in the adult of Scyllium catulus. In 
two figures of the adult, Parker, however, shows a small pitui- 
tary fossa which lodges the pituitary body and is separated 
from the so-called infundibulum by a tall preclinoid wall. I 
have heretofore always considered this condition in this fish 
to be either an abnormality in the particular specimen ex- 
amined by Parker, or a condition due to great age, for Parker 
shows both the preclinoid and postclinoid walls strongly calci- 
fied. I have, however, now examined two small adults of this 
fish, and I find the canalis transversus of Gegenbaur’s descrip- 
tions occupying exactly the position of Parker’s pituitary fossa, 
