=The Suspensorium of the Mandible.=--The lower jaw is attached to the cranium by a chain of suspensory bones, which vary a good deal with different groups of fishes. The articular is jointed with the flat quadrate bone (19), which lies behind the pterygoid. A slender bone passes upward (18) under the preopercle and the metapterygoid, forming a connection above with a large flattish bone, the _hyomandibular_ (17), which in turn joins the cranium. The slender bone which thus keys together the upper and lower elements, hyomandibular and quadrate, forming the suspensorium of the lower jaw, is known as _symplectic_ (18). The hyomandibular is thought to be homologous with the stapes, or stirrup-bone, of the ear in higher animals. In this case the symplectic may be homologous with its small orbicular bone, and the malleus is a transformation of the articular. The incus, or anvil-bone, may be formed from part of Meckel's cartilage. All these homologies are however extremely hypothetical. The core of the lower jaw is formed of a cartilage called Meckel's cartilage, outside which the membrane bones, dentary, etc., are developed. This cartilage forms the lower jaw in sharks, true jaw-bones not being developed in these fishes. In lampreys and lancelets there is no lower jaw. =Membrane Bones of Face.=--The membrane bones lie on the surface of the head, when they are usually covered by thin skin and have only a superficial connection with the cranium. Such bones, formed of ossified membrane, are not found in the earlier or less specialized fishes, the lancelets and lampreys, nor in the sharks, rays, and chimæras. They are chiefly characteristic of the bony fishes, although in some of these they have undergone degradation. The _preorbital_ (49) lies before and below the eye, its edge more or less parallel with that of the maxillary. It may be broad or narrow. When broad it usually forms a sheath into which the maxillary slips. The _nasal_ (51) lies before the preorbital, a small bone usually lying along the spine of the premaxillary. Behind and below the eye is a series of about three flat bones, the _suborbitals_ (50), small in the striped bass, but sometimes considerably modified. In the great group of loricate fishes (sculpins, etc.), the third suborbital sends a bony process called the suborbital stay backward across the cheek toward the preopercle. The suborbital stay is present in the rosefish. In some cases, as in the gurnard, this stay covers the whole cheek with a bony coat of mail. In some fishes, but not in the striped bass, a small supraorbital bone exists over the eye, forming a sort of cap on an angle of the frontal bone.