SKELETON 



87 



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 (figs. 85, 87-89) have a considerable range of skull structure. 

 In the lower groups like siluroids and cyprinids, the chondrocranium is largely 

 persistent and the cranial cavity extends into the ethmoid region as in the 

 higher ganoids. In other teleosts the trabeculae are approximate between the 

 orbits (tropibasic) and develop a thin interorbital septum which limits the 

 anterior end of the cranial cavity. 

 The cartilage bones are more numer- 

 ous. All four occipitalia are present, 

 the occipital condyle being formed 

 by basi- and exoccipitals. Basi, ali-, 

 and orbitophenoids occur, and besides 

 ectethmoids a pair of mesethmoid ossi- 

 fications. In the otic capsule there are 

 usually pterotic and sphenotic ossifi- 

 cations. 



The cranial roof is largely formed 

 by the frontals and parietals, the 

 latter frequently separated by a strong 

 process of the supraoccipital. Several 

 of the cartilage bones are visible from 

 above. The roof of the mouth is 

 formed by the large parasphenoid and 

 the vomers. Premaxillaries (rarely 

 lacking) and maxillaries form the upper 

 jaw, both usually bearing teeth, but 

 occasionally, by overdevelopment of 

 the premaxillary, the maxillary is ex- 

 cluded from the margin of the jaw. 



Instead of the single pterygoid of 

 higher vertebrates there are three 

 bones, an entopterygoid adjoining the 

 palatine, a mesopterygoid (ectoptery- 

 goid) which extends back to the quad- 

 rate, and a metapterygoid above the 

 quadrate (fig. 89). When the hyo- 

 mandibular cartilage ossifies it forms 



a hyomandibular bone from its upper portion and a symplectic (an element not 

 known outside the teleostomes), which supports the quadrate. A small bone, 

 the interhyal, intervenes between the hyomandibular and the rest of the hyoid. 

 he hyoid copula consists of several elements, the anterior, which supports the 

 tongue being called the entoglossal, the posterior, which connects with the bran- 

 chial arches, the urohyal. The fifth gill arch consists of a single element on 

 either side, the hypopharyngeal bone, which usually bears teeth, the hypo- 

 pharyngeals of the two sides being fused in the plectognaths, forming a pharyn- 



FiG. 88. — Dorsal view of skull of 

 mackerel, Scomber, after Allis; letters as in 

 fig. 8s. 



