242 



ZOOLOGY 



SECT. 



B 



lam. 



art 



cartilage of the posterior 

 part are a pair of small 

 replacing bones which 

 appear to represent the 

 most anterior of the 

 spinal elements fused 

 with the skull. On Ihr 

 upper surface, an- two 

 unpaired (A and B) and 

 four paired (C and -sv/.) 

 investing hones, the 

 homologies of all of 

 which are undetermined. 

 Premaxillse, maxillae, 

 and nasals are absent. 

 On the ventral surface 

 is a large investing bone 

 (Fig. 917, P.Sph.) repre- 

 senting the parasphenoid 



FiQ. 916. Cratodu forsteri. Dorsal view of the n f +}, TplpnQfnmi Tn 



skull. A, anterior median investing bone fart, articular ( 



surface for second fin-ray ;B, posterior median investing front IS a pair of Small 

 bone ; C, inner lateral investing bone ; lab. labial car- , , f , 



tilages ; lam. process projecting over gills ; op. oper- upper labial Or nasal 



culum ; pr. orb. pre-orbital process of chondrocranium ; _<.: !_,..-_ A ^olof^ 



eb. or. sub-orbital bones; gq. outer lateral investing Cartilages. A palatO- 



quadrate cartilage (Fig. 



915, pal), firmly fixed to the side-wall of the cranium, gives attach- 

 ment to the mandible, so that 

 the skull is autostylic ; the quad- 

 rate element is distinct in the larva 

 and independently developed. 

 In front the palatoquadrate 

 contains a palatopterygoid ossi- 

 fication which forms the support 

 for the large composite tooth of 

 the upper jaw. The mandible 

 consists of Meckel's cartilage with 

 an angular bone behind, and a 

 large splenial, which bears the 

 tooth, in front. The dentary is 

 vestigial. The hyomandibular is 

 only represented by a small 

 vestige. Opercular (op.) and in- 

 teropercular (int.) bones support 

 the operculum. The hyoid (hy.) 

 and branchial arches (br.) are 

 cartilaginous. Of the latter, four 

 are completely developed, and a 

 fifth is represented by a vestige. 



FKJ. 'J17. Ceratodus forateri. Ventral 

 view of the skull, c, occipital rib ; d, 

 palatine teeth ; d', vomeritie teeth ; na. 

 anterior and posterior nares ; P. palatine 

 region of palatopterygoid ; P. Sph. para- 

 sphenoid ; PL pterygoid; Qu. quadrate 

 region ; Vo. vomer. (From Dean, after 

 Gttnther.) 



