All are well developed in the striped bass and in most fishes. In some specialized forms they are much distorted, coossified, or otherwise altered, and their relations to each other may be more or less changed. In the lower forms they are not always fully differentiated, but in nearly all cases their homologies can be readily traced. In the sharks and lampreys the skull constitutes a continuous cartilaginous box without sutures. In the dipnoans and other forms having a bony casque the superficial bones outside the cranium may not correspond to the cartilaginous elements of the soft skull itself. [Illustration: FIG. 25--_Roccus lineatus._ Posterior view of cranium. 6. Parietal. 7. Epiotic. 8. Supraoccipital. 9. Pterotic. 10. Opisthotic. 11. Exoccipital. 12. Basioccipital.] =Bones of the Jaws.=--The bones of the jaws are attached to the cranium by membranes only, not by sutures, except in a few peculiarly specialized forms. _The Upper Jaw._--The _premaxillary_ (32) lies on either side and forms the front of the upper jaw. Its upper posterior tip or premaxillary spine projects backward almost at right angles with the rest of the bone into a groove on the ethmoid. There is often a fold in the skin by which this bone may be thrust out or protracted, as though drawn out of a sheath. When the spines of the premaxillary are very long the upper jaw may be thrust out for a considerable distance. The premaxillary is also often known as intermaxillary. Lying behind the premaxillary, its anterior end attached within the angle of the premaxillary, is the _maxillary_ (31), or _supramaxillary_, a flattened bone with expanded posterior tip. In the striped bass this bone is without teeth, but in many less specialized forms, as the salmon, it is provided with teeth and joined to the premaxillary in a different fashion. In any case its position readily distinguishes it. In some cases the maxillary is divided by one or more sutures, setting off from it one or more extra maxillary (supplemental maxillary) bones. This suture is absent in the striped bass, but distinct in the black bass, and more than one suture is found in the shad and herring. The roof of the mouth above is formed by a number of bones, which, as they often possess teeth, may be considered with the jaws. These are the _palatine_ bones (21), one on either side flanking the vomer, the _pterygoid_ (20), behind it and articulating with it, the _mesopterygoid_ (22), on the roof of the mouth toward the median line, and the _metapterygoid_ (23), lying behind this. Although often armed with teeth, these bones are to be considered of the general nature of the membrane bones. In some degraded types of fishes (eels, morays, congers) the premaxillary is indistinguishable, being united with the vomer and palatines. [Illustration: FIG. 26.--_Roccus lineatus._ Face-bones, shoulder and pelvic girdles, and hyoid arch.