As regards the general structure of the skull and the nature and disposition of its cartilage- and membrane-bones, the remaining living Teleostomi have much in common with the Salmon. In all the skull is hyostylic, and, unlike the Chondrostei, each half of the primitive upper jaw remains distinct from its fellow, and is separately articulated in front with the lateral ethmoid of the same side by its palatine element. The palato-quadrate cartilage is always more or less completely replaced by bones similar to those of the Salmon, and although they often carry teeth, as a rule they do little more than constitute a rigid buttress for the fixation of the quadrate condyle for the lower jaw. The secondary upper jaw is nearly always well developed, and includes a premaxilla as well as a maxilla on each side. There are, however, certain features in each of the minor groups which are either distinctive or highly characteristic. In the surviving Crossopterygii (e.g. _Polypterus_[199]) the chondro-cranium is complete in the ethmoidal and post-orbital regions, except where it has been partially replaced by cartilage bones, but in the inter-orbital region the continuity of the roof is interrupted by a large fontanelle, which is only closed by the investing frontal bones (Fig. 132, C). There is also a large basi-cranial fontanelle in the sphenethmoid, closed, however, by the underlying parasphenoid. A large "occipital" bone continuously ossifies in the occipital cartilage and completely surrounds the foramen magnum. {227}[Illustration: FIG. 132.—A, side view of the skull of _Polypterus_; B, dorsal view, showing the chief dermal bones; C, similar view of the chondro-cranium after the removal of the dermal bones. _An_, Angular; _Ar_, articular; _D_, dentary; _E_, mesethmoid; _f.m_, foramen magnum; _Fr_, frontal; _l.e_, lateral ethmoid; _Mx_, maxilla; _Na_, _Na′_, nasal and accessory nasal bones; _occ_, occipital; _ol_, nasal aperture; _Op_, operculum; _op.o_, opisthotic; _O.t_, _os_ terminate; _Pa_, parietal; _Pm.x_, premaxilla; _P.t_, post-temporal; _Ptf_, post-frontal; _Qu_, quadrate; _S.b_, _S.b′_, circum-orbital ossicles; _S.Op_, sub-operculum; _Sp_, splenial; _sp.eth_, sphenethmoid; _sp.o_, sphenotic; _Spr_, spiracular ossicles, between which is the spiracle; _S.t_, supra-temporals; _Y_, cheek-plate (pre-operculum); _Y′_, _Y″_, smaller cheek-plates; _z_, _z_, _z_, _z_, post-spiracular ossicles; _z′_, _z′_, prespiracular ossicles. In C the cartilage is dotted. (From Traquair.)]