SKULL — TELEOSTS 



Membrane bones are greatly reduced, or even completely absent 

 from Plectognaths and Pediculati. In other fishes the frontal 

 (paired in development, fusing early) is the largest membrane bone 

 on the dorsal surface. In Physostomes it extends from supraoccip- 

 itals to nasals, or, when these are separate, to the supraethmoid. 

 In most Physoclists the parietals come between supraoccipital and 

 frontal, and rarely (Mormyris) an interparietal also occurs. Fre- 

 quently anterior and posterior ends of the frontal are incised by 

 narrow fontanelles, and in a few forms the frontal is excluded from 

 the wall of the cranial cavity. Its participation in the anterior wall 

 of the cavity was noted above (p. log). The Siluroids excepted, 



Fig. ii6. — Interior of cranium of Amiurus (Kindred, '19). as, alisphenoid; bo, 

 basioccipital; eb, epiphysial bar; eo, exoccipital; /, frontal; ns, nasal septum; os, orbito- 

 sphenoid; pro, prootic; ps, parasphenoid; se, supraethmoid; so, supraoccipital; spo, 

 sphenotic; sqp, squamoso-pterotic; v, vomer. 



the parietals are paired, though reduced in Synentognaths. Pre- 

 and postfrontals, supraethmoid and squamosals are noticed with the 

 cartilage bones. 



The circumorbital bones (fig. loo) arise as protection to the lateral 

 hne canals and in the more primitive Teleosts are tubular. Of them 

 the supraorbitals are least constant, and when present, are small. 

 There are usually four infraorbitals. Some of these are enlarged 

 in Loricati into plates which give the name 'mail-cheek' fishes to 

 this group. The last infraorbital has a 'stay,' a strong process 

 extending back as a support for the spine of the preoperculum. 



The bones (premaxilla and maxilla) of the upper jaw afford 

 characters utilized in systematic ichthyology. Usually the maxilla is 

 the longer and in a few cases, (recalhng Lepidosteus) is divided into 

 two or more ossicles. On the other hand it is lacking in a few species 

 (some Siluroids, Anguilla, etc.). In Acanthopterygii, Anacanthini, 

 some Pharyngobranchs, Cyprinoids, etc. the maxilla is medial to and 



