114 VERTEBRATE SKELETON 



Part of the dentale is described as arising from cartilage (possibly a 

 mentomeckelian) and it frequently has a vacuity on the medial side. 



As in Ganoids, the hyoid arch consists of the suspensor and the 

 hyale, the latter extending into the floor of the mouth. At most, the 

 suspensor consists of hyomandibula and symplectic (the latter absent 

 in some Physostomes). The hyomandibula is firmly fixed to the 

 cranium (not ankylosed) in Plectognaths; elsewhere it is movable. 

 Sometimes it has a single head which articulates with the opisthotic; 

 others have also an anterior head which connects with the sphenotic 

 or even as far forwards as the alisphenoid. It articulates in front 

 with the metapterygoid ; below either with the quadrate directly or 

 by a symplectic which varies in size. 



A small interhyal (stylohyal) connects hyomandibula and hyale. 

 The hyale is divided into epi-, cerato- and hypohyal, the latter 

 element of the two sides being connected by a basihyal which some- 

 times extends as an entoglossum into the tongue, this sometimes 

 covered by a dermentoglossum, arising by the fusion of dentinal 

 bases. The opercular apparatus is connected with the hyoid arch, 

 its parts and relations suggesting homology with the hyoid radials 

 of Elasmobranchs, a comparison negatived by the dermal origin of 

 the opercular bones. The operculum, when fully developed, has the 

 parts enumerated above (p. 98). The operculare is hinged to a 

 process on the posterior side of the hyomandibula, the suboperculum 

 being connected by membrane to operculare and interoperculum. 

 The branchiostegal bones are usually slender, sometimes one or more 

 are expanded to broad plates. Some Elopids have gular plates. 

 The branchial arches, usually five, are reduced at the hinder end of 

 the series. Typically each is divided as in sharks, (p. 65), the 

 halves of each arch being connected ventrally by a basibranchial. 

 The pharyngobranchials (suprabranchials) usually he longitudinally 

 and side by side, beneath the cranium and not infrequently all are 

 fused to a single suprapharyngeal bone. Usually they bear teeth 

 and in Cyprinoids they receive support from a projection from the 

 floor of the skull. These suprapharyngeals act in opposition to the 

 cerato- and hypobranchials (inferior pharyngeals), both serving as 

 pharyngeal jaws, the resemblance to true jaws being greatest in the 

 Pharyngognaths where the lower bones of the two sides unite to a 

 single plate. The teeth on these pharyngeals are supported on 

 plates of membrane bone (superior and inferior dermopharyngeals), 



