456 J. FRANK DANIEL 
palato-quadrate (p-q.); the lower segment is the mandibular 
or Meckel’s cartilage (md.). In Heterodontus this arch is closely 
attached to the cranium in the preorbital region by a capsular 
ligament which keeps the upper and anterior margin (a.p.) 
of the palato-quadrate in the palatal fossa of the cranium. <A 
slip from the capsular ligament (c.l.’ fig. 7), arising along the 
ventral margin of the cranium under the fossa (*fig. 2), extends 
backward and downward to join the quadrate on the ventral 
part of the transverse median ridge (tr.m.r.). Just under the 
orbit both the upper and the lower segments of the mandibular 
arch flare outward in Heterodontus francisci so that the distance 
to the spiracular cartilage or to Huxley’s so-called otic process 
is, I take it, greater than that described by Huxley for Hetero- 
dontus philippi. Posteriorly, the arch has no direct attachment 
to the cranium but is held in position by ligaments soon to be 
described. 
As a cartilage the palato-quadrate (p-q., figs. 6 and 7) is longer 
than the mandible. Its upper margin is irregular, due princi- 
pally, to a dorsal indenture in the anterior third. The anterior 
wall of this indenture comes in contact with the ethmoidal 
region, while the posterior wall of the indenture, as seen in 
figure 7 (a.p.) serves as a process of the palato-quadrate which 
fits into the palatal fossa of the cranium. Medially from this 
articular surface a sharp ridge (tr.m.r.) runs, to the lower 
part of which is attached the slip from the capsular ligament 
above described. Externally, at the beginning of the posterior 
third of the quadrate there is a strong lateral transverse ridge 
which passes almost across the cartilage:(tr.l.r., fig. 6). To 
this ridge are attached tendinous fibers of the adductor man- 
dibularis muscle. Posteriorly and dorsally the palato-quadrate 
is provided with a lateral flattened enlargement, the hyal process 
(hl.p.), also for muscular attachment. The hyal process is 
continuous with a similar process on the mandible. 
The mandible (md., figs. 6 and 7) is an unusually heavy 
cartilage. The angular part of this is high, considerably elevat- 
ing the quadrato-mandibular joint. If seen from below, the man- 
dible would appear as a strongly crescentic cartilage, the poste- 
