90 



COMPARATIVE ANATOMY 



of Teleosts (p. 92) also occur in connection with the palatoquad- 

 rate and the entire visceral skeleton, including Meckel's cartilage 



and the branchial arches. 

 Though still largely re- 

 tained, especially in Amia, 

 the cartilage thus becomes 

 relatively reduced as com- 

 pared with the cartilagin- 

 ous Ganoids (Fig. 68, B). 



At the posterior end of 

 the trabeculge, which only 

 remain separated from one 

 another by a narrow slit, 

 a lateral basipterygoid 

 process arises in Lepidos- 

 teus for articulation with 

 the palatoquadrate arch, 

 which is thus connected 

 with the skull not only 

 indirectly, through the 

 hyomandibular, but also 

 directly. 



The opercular bones are 

 more highly developed than 

 in cartilaginous Ganoids, 

 and may include an oper- 

 culum, a preoperculum, a 

 suboperculum, and an in- 

 teroperculurn as well as 

 branchiostegal rays : these 

 in part correspond to in- 

 vesting bones of the carti- 

 laginous byoid rays. A 

 symplectic, an interopercu- 

 lum, and branchiostegal 

 rays are wanting in Poly- 

 pterus. 



The branchial skeleton 

 in Ganoids consists of four 

 or five more or less strong- 

 ly ossified and segmented 

 gill-arches, decreasing in 

 size antero - posteriorly 

 (Fig. 67) ; in Bony Ganoids 

 the surface which looks towards the throat is beset with teeth. 



The Ganoidei are of special interest, as they, with the Elasmo- 

 branchii, constitute almost the entire Fish-fauna through the 

 Silurian, Devonian, and Carboniferous periods, and as the Teleostei, 



Fin. 68A. SKULL OF Polypter-u* Iiirkir FROM 

 THE DORSAL SIDE. 



a, b, c, (I, supraoccipital shields. The two 

 arrows pointing downwards under the 

 spiracular shields show the position of 

 the openings of the spiracles on to the 

 outer surface of the skull. F, frontal ; 

 M, maxilla; N, nasal; Xa, external 

 nostril ; Op, operculum ; Or!>, orbit ; 1\ 

 parietal ; Pm.c, prenmxilla : PO, pre- 

 operculum; Sb, Sl>', anterior and posterior 

 suborbital ; SO, suboperculum ; Sj), pre- 

 spiracular bones. 



