44 The Skeleton of the Fish 



with a large flattish bone, the hyomandibnlar (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 sym- 

 plcctic (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 ex- 

 tremely 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 wnth 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 chimeras. 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 pre- 

 orbital, a small bone usually lying along the spine of the pre- 

 maxillary. 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. 



The largest uppermost flat bone of the gill-covers is known 



I 



