228 
lateral wall of this large pituitary fossa, at about the middle of its 
length, is the large internal opening of the efferent pseudobranchial 
foramen, a slight groove in the cartilage marking the short course of 
the artery after it enters the cranial cavity and before it falls into 
the internal carotid. Dorsal and slightly anterior to this foramen, 
in the lateral wall of the cranial cavity and not in that of the pitui- 
tary fossa, is the foramen oculomotorium, and antero-dorsal to this 
latter foramen, near the roof of the cranial cavity, is the foramen 
trochleare. 
The posterior third, approximately, of the large pituitary fossa 
of the prepared skull is slightly deeper than the remainder of the 
fossa and has the appearance of being a somewhat separate and in- 
dependent fossa; and in certain of the selachians described by GEGEN- 
BAUR the corresponding part of the chondrocranium is shown and 
described by that author as a part, or region, of the cartilage of the 
basis cranii that lies beneath the hind end of the pituitary fossa and 
does not in any way form a part of it. In two of the four specimens 
of Chlamydoselachus that I have examined, this posterior part of 
the fossa had the same width as the anterior portion, but in the other 
two specimens it was considerably constricted by lateral growths of 
cartilage to be described below. In the two former specimens there 
was, on either side, in the lateral wall of this posterior third of the 
large pituitary fossa, a large deep conical pit, at the apex of which 
was the foramen for the pituitary vein, this foramen being the orbital 
opening of the canalis transversus of GEGENBAUR’S descriptions of 
other selachians, a canal which I shall refer to as the pituitary canal, 
although, in Chlamydoselachus, it is not enclosed in cartilage. Imme- 
diately anterior to this pituitary canal, and close to the median line, 
the internal carotid artery perforated the cartilage of the basis eranii 
and opened into a small median pit, or transverse groove, which lodged 
the related portions of the carotid arteries of opposite sides together 
with the short cross-commissural canal that here connects them 
(Auuıs, 1911), the anterior edge of the pit or groove marking the 
anterior edge of this posterior and deeper portion of the entire fossa. 
This deeper portion of the fossa was filled, in both these specimens, 
with tough connective tissue such as is described by GEGENBAUR 
and shown by him in his median views of the chondrocrania of 
Hexanchus, Mustelus and Galeus, this tissue, in Chlamydoselachus, 
completely enveloping and surrounding both the carotid arteries and 
