Die FISHES CHAP. 
been remarked that it “dominates the whole body, everything 
else yields to it.’ Meckel’s cartilages are represented either 
by the cornual cartilages, as seems most probable, or by the 
dental plate (Fig. 125, ec. and D). 
In the generality of Elasmobranchs the skull resembles that 
of the Dog-Fish in essential structure. The more important 
modifications within the limits of the group relate to differences 
in the mode of attachment of the primitive upper jaw to the 
skull, and the number of branchial arches. In most Elasmo- 
branchs the skull is hyostylic, as in Scylliwm, but there are 
pe. orb 
Fig. 128.—Lateral view of the skull of Notidanus (Heptanchus) cinereus ; mck, Meckel’s 
cartilage, or primitive lower jaw; pal.qu, palato-quadrate cartilage or primitive 
upper jaw ; pt.orb, post-orbital process of the cranium with which the post-orbital 
process of the palato-quadrate articulates. (From Parker and Haswell, after 
Gegenbaur. ) 
two genera which, in different ways, are exceptions to this rule. 
In Notidanus the hinder part of each palato-quadrate cartilage 
grows upwards into a strong post-orbital process, which articulates 
with the suitably modified post-orbital process of the periotic 
capsule (Fig. 128); hence the primitive upper jaw acquires a direct 
dorsal connexion with the cranium, and, as the hyoid arch is now 
relieved from taking any part in its support, the hyomandibular 
is reduced to the condition of a relatively slender rod of cartilage. 
By this arrangement both the mandibular and hyoid arches have 
their own separate and independent connexions with the cranium, 
and the skull is said to be amphistylic.. The Port Jackson Shark 
1 Huxley, P.Z.S. 1876, p. 40, et seq. 
