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the pituitary vein. This tough tissue was covered dorsally by, and 
was continuous with, the tough glistening membrane that everywhere 
lined the walls of the cranial cavity, the cerebral surface of this mem- 
brane here being presented dorso-anteriorly, as it is also shown to 
be, in GEGENBAUR’S figures, in each of the three selachians just 
above mentioned. Overlying this membrane, in Chlamydoselachus, 
and extending throughout the entire length of the pituitary fossa, 
there was a relatively thin layer of loose connective tissue, and on this 
tissue, and oceupying the full length of the fossa, was the pituitary 

Lepidosteus Scomber Amia 
Fig. 1. Diagrammatic representation of the several stages in the development 
of the trigemino-facialis chamber in fishes. 
ec, external carotid artery. ijv, internaljugular vein. pf, ramus palatinus facialis. 
body, the hind end of that body, the region of the saccus vasculosus, 
overlying the membrane that spans the space occupied by the pituitary 
canal. The membranes overlying this latter canal were pierced by 
one or more openings which doubtless transmitted branches of the 
pituitary vein, but these veins could not be traced in my dissections. 
The internal carotid artery of either side, after its anastomosing 
connection with its fellow of the opposite side, pierced the tough 
glistening membrane and then ran forward in the overlying loose 
