10 BULLETIN OF THE 
The upper jaw, quadrato-pterygoid (q-pg), is a broad, thin, twisted 
blade, a trifle over five inches in length. Anteriorly it is spatulate, near 
seven tenths of an inch in width, and is twisted so as to rest obliquely 
under the skull, the lower edge being turned outward. Posteriorly it is 
more than an inch in width, strongly convex on the inner side, deeply 
concave on the outer, and at the articulation with the meckelian is 
twisted half-way around so as to bring the side of the extremity in 
contact with the latter. An inch and three quarters back from its front 
end it bears a strong, compressed, palatal or trabecular process (tp). 
This process is a little more than half an inch in height, a little less in 
width, and is rounded on its upper edge, where it is attached by ligament 
to the skull near the top of the orbital cavity. Its outer and inner faces 
are convex ; the latter being received in a concave articular depression 
in the skull. At the sides and beneath, this concavity has been enlarged 
by ridges of cartilage. Half an inch from the hinder end the pterygo- 
quadrate bears a small hyal process, which is overlaid by a similar one 
on the hyomandibular. Two inches from the same end there is a larger 
process, quadratic or otic (gp), formed by a short bend in the thin 
upper edge. Some of the most prominent differences between Chlamy- 
doselachus and the Notidanidze are to be seen in the attachments and 
articulations of this cartilage. 
The lower jaw, Meckel’s cartilage (mk), is a strong, broad, twisted 
cartilage. It is broad posteriorly, and tapers gradually forward to near 
the end, where it decreases in size rapidly and presents but a small sur- 
face to its fellow from the opposite side at the symphysis. It is twisted 
in front to bring the sharp upper edge outward, where the cartilage 
bends inward toward the middle of the snout. In the posterior two 
thirds of the length the lower border is wide, with a sort of flange ; for- 
ward the outer edge of this flange fades into the middle of the blade, 
while the inner continues as the inner edge. Backward the lower jaw 
is convex on the inner side, and deeply concave on the outer. Bending 
outward at the end, the articulation of the pterygo-quadrate with this 
cartilage has the appearance of taking place on the upper edge. 
The Ceratohyals (chy) are moderately slender, curved, club-shaped or 
bilotate anteriorly, and tapering in the posterior two fifths of their 
length, where applied and attached by ligament to the meckelians. 
Though the thick front lobe articulates with the side of the basihyal, 
the outer and thinner lobe underlies the hinder angle of that cartilage. 
The latter reaches back above the ceratohyal to articulate with the first 
ceratobranchial. In the figure the lobe has been brought too far back, 
and too near its fellow on the opposite side of the basihyal. 
