SKELETON. 



79 



In other ganoids (holosteans and crossopterygians) the skull is much like that 

 of the teleosts, differing in the extension forward of the cranial cavity. There are 



na 



FIG. 78. Median section of skull of mackerel (Scomber) after Allts. For letters see fig. 68. 



one (Amia) or two (Polypterus} gular bones developed between the rami of the 

 lower jaw, and in Polypterus parietals, frontals and nasals fuse with age, and there 

 are numerous small bones in the cranial roof, developed along the lateral line 

 canals. Amia has several splenials in 

 the lower jaw. 



TELEOSTS (fig. 76-80) have a consider- 

 able range of skull structure. In the lower 

 groups like siluroids and cyprinids, the 

 chondrocranium is largely persistent and 

 the cranial cavity extends into the eth- 

 moid region as in the higher ganoids. 

 In other teleosts the trabeculae are ap- 

 proximate between the orbits (tropibasic) 

 and develop a thin interorbital septum 

 which limits the anterior ends of the 

 cranial cavity. The cartilage bones are 

 more numerous. All four occipitalia are 

 present, the occipital condyle being formed 

 by basi- and exoccipitals. Basi-, ali-, and 

 orbitophenoids occur, and besides ecteth- 

 moids a pair of mesethmoid ossifications. 

 In the otic capsule there are usually 

 pterotic and sphenotic ossifications. 



The cranial roof is largely formed by 

 the frontals and parietals, the latter fre- 

 quently separated by a strong process of 

 the supraoccipital. Several of the car- 

 tilage bones are visible from above. The 

 roof of the mouth is formed by the large 

 parasphenoid and the vomers. Premaxil- 

 laries (rarely lacking) and maxillaries FlG . 79 . Dorsal view of skull of mack- 

 form the upper jaw, both usually bearing erel, Scomber, after Allis; letters as in fig. 68 



