. Annals of the New York Academy of Sciences. Science. ADAMS, PHYLOGENY OF THE JAW MUSCLES 81 This small cartilage, then, represents the hyomandibular and the sym- plectic of the teleosts. It is in the correct position for these bones and there is little doubt of the homology. With its reduction there has been quite a change in the opercular region, as the opercular bones are reduced and changed together with the preopercular. Giinther thought that a small bit of cartilage on the anterior edge of the opercular was the vestige of the preoperculum. Goodrich (1909, pp. 237-238) says: It is in the
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. Annals of the New York Academy of Sciences. Science. ADAMS, PHYLOGENY OF THE JAW MUSCLES 81 This small cartilage, then, represents the hyomandibular and the sym- plectic of the teleosts. It is in the correct position for these bones and there is little doubt of the homology. With its reduction there has been quite a change in the opercular region, as the opercular bones are reduced and changed together with the preopercular. Giinther thought that a small bit of cartilage on the anterior edge of the opercular was the vestige of the preoperculum. Goodrich (1909, pp. 237-238) says: It is in the connection of the skull with the visceral arches that the dipnoi have diverged most conspicuously from the other fishes. The modern genera are completely autostylic. The pterygo-quadrate bar is firmly fused to the cranium in front and behind. The spiracle disappears and the hyoid arch is well developed, with a medial basihyal, paired hypohyals and large ossified ceratohyals. But the hyomandibular takes no share in the support of the jaws. It disappears, indeed, entirely in the Dipneumones where the cerato- hyals alone remain, and, as Huxley showed, is represented in Ceratodus by a minute vestigial cartilage, overlying the hyomandibular branch of the seventh nerve. The skull of Ceratodus has a continuous dermal temporal roof as in the stegocephalians. Parts of the skull resemble the cartilaginous struc- ture in the urodele embryo, especially in the region of the arches, but here the re- semblance stops. In the arrangement of the jaw muscles this dipnoan is very simple. The skull con- sists of a massive cartilag- inous part with a covering of dermal bones which gives the head its large size. The space between the cartilage surrounding the brain and the dermal bone is filled with the enormous temporal muscle which supplies the motive power for the great crushing apparatus. The general aspect of the head is amphibian-like to an extent found in no other fish but the eels. There is