SKULL GANOIDS I05 



replaced by a number of 'cheek bones.' Parasphenoid and vomer 

 are long and slender, and the pterygoquadrate series has the quadrate 

 shifted to the anterior end of the entopterygoid, bringing the hinge 

 of the jaw some distance in front of the orbit. The hyomandibula 

 is movably attached to the otic capsule; it articulates below with a 

 slender symplectic which has no connexion with the quadrate except 

 by way of the interoperculum. The five branchial arches are well 

 developed except the last which consists of a single element, appar- 

 ently the fused cerato- and hypobranchial. The broad basihyal, 

 covered dorsally by bone, extends into the tongue as an ps ento- 

 glossum. The pharyngobranchials of arches 2 to 4 are divided into 

 superior and inferior elements, and all of the arches are connected 

 with the posterior part of the cranium. 



TELEOSTEL— This great group, with its thousands of species, 

 shows a great variety in form of skull, but the differences are largely 

 those of form, less of presence or absence or different relations of the 

 separate bones. The lower groups are much like the Holostei, the 

 Hne between them being negligible so far as skull is concerned. From 

 the lower Teleosts there is a gradual progress through the whole 

 series to the most specialized forms. Hence it is impossible, without 

 greatly exceeding the hmits of the present work, to begin to enumer- 

 ate all of the conditions which occur. In fact, the lower members 

 of the group are better known than the higher and more aberrant 

 forms, and there has been no general survey of our knowledge for 

 years. No group of Vertebrates needs a comparative study more 

 than do the Teleosts,. 



The development of the skull has been studied in few species and those 

 mostly Physostomes (p. 92) where the structure is much like that of Amia. 

 In these the cranium is platybasic (fig. 96), the cranial cavity extending to the 

 ethmoid region. The higher species have a tropibasic cranium (fig. 97), the 

 great development of the orbits so constricting the skull in the interorbital region 

 that the brain cannot extend beyond the alisphenoid bones. 



The otic capsules sometimes arise in continuity with the parachordal plates, 

 sometimes independently. Several vertebrae {Carassius 3, Salmo 5) are absorbed 

 in the occipital region. The trabecule at first are in a plane with the basal 

 plate, and in front they unite in a broad ethmoid plate which extends laterally 

 beneath the nasal organs. In platybasic crania the trabeculae are distinct as 

 far forwards as the ethmoid plate; in tropibasic they unite to a trabecula com- 

 munis a Httle in front of the hypophysis. 



There may be several fenestras in the chondrocranial floor, among them a 

 basicapsular between the parachordal and otic capsule, the ninth nerve in some 



