Page:An Introduction to the Study of Fishes.djvu/118

90 (26), connected by means of the metapterygoid (27) with the ecto- (24) and ento-pterygoid (25), the foremost bone of the arch being the palatine (22). All these bones have been sufficiently described above (p. 55), and it remains only to be mentioned that the bones of the palatine arch are but rarely absent, as for instance in Murænophis; and that the symplectic does not extend to the articulary of the mandible, as in Amia and Lepidosteus, though its suspensory relation to the Meckelian cartilage is still indicated by a ligament which connects the two pieces. Of the mandibulary bones the articulary (35) is distinctly part of Meckel's cartilage. Frequently another portion of cartilage below the articulary remains persistent, or is replaced by a separate membrane-bone, the angular.

4. Membrane-bones of the alimentary portion of the visceral skeleton of the skull.—The suspensorium has one tegumentary bone attached to it, viz. the præoperculum (30); it is but rarely absent, for instance in Murænophis. The premaxillary (17) and maxillary (18) of the Teleostei appear to be also membrane-bones, although they are clearly analogous to the upper labial cartilages of the Sharks. The premaxillaries sometimes coalesce into a single piece (as in Diodon, Mormyrus), or they are firmly united with the maxillaries (as in all Gymnodonts, Serrasalmo, etc.) The relative position and connection of these two bones differs much, and is a valuable character in the discrimination of the various families. In some, the front margin of the jaw is formed by the premaxillary only, the two bones having a parallel position, as it has been described in the Perch (p. 53); in others, the premaxillary is shortened, allowing the maxillary to enter, and to complete, the margin of the upper jaw; and finally, in many no part of the maxillary is situated behind the premaxillary, but the entire bone is attached to the end of the premaxillary, forming its continuation. In