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Fio. 905.— Ceratodus forsteri. Dorsal view of the 

 skull. A, anteriiii- median iuvestiug bone ; art. articular 

 surface for second fin-ray ; B, posterior median investing 

 bone ; V, inner lateral investing bone ; hijb. labial car- 

 tilages ; Uxhi. process projecting over gills ; op. oper- 

 culum ; jO)-. oy\>. preorbital process of chondrocrauium ; 

 »>>. orb. suborbital bones ; sq. outer lateral investiuff 

 bone. (After Hu.xJey.) 



absent. On the ven- 

 tral surface is a larae 

 iuvestinL( bone (Fig. 

 906, P. S'jih.) represent- 

 ing the parasphenoid 

 of the Teleostoiui. In 

 front is a pair of small 

 upper labial or nasal 

 cartilages. A palato- 

 quadrate cartilaofe fFio- 

 *di)-\:, inil.), 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 in- 

 dependently developed. 

 In front the palato- 

 (juadrate contains a 

 palatopterygoid ossifi- 

 cation which forms the 

 support for the large 

 composite tooth of the upper jaw. The hyomandibular is only 



represented by a small vestige. 

 Opercular {of.) and interoper- 

 cular {int.) bones support the 

 operculum. The mandible con- 

 sists of Meckel's cartilage with 

 an angular bone behind, and a 

 large splenial, which bears the 

 tooth, in front. The dentary is 

 vestigial. The hyoid {hy.) and 

 branchial arches '(hr.) are cartil- 

 aginous. Of the latter, four are 

 completely developed, and a fifth 

 is represented by a vestige. There 

 are no branchial rays, but the 

 branchial arches bear a series of 

 gill-rakers with cartilaginous 

 supports. 



The pectoral arch (Fig. 904, 

 2Jct.) is a stout cartilage with two 

 pairs of investing bones, the 

 clavicles on the coracoid, and the 

 cleithra on the scapular regions. 



Fio. 006.- Ceratodus forsteri. Ventral 

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

 lialatine teeth ; ,X, vomerine teeth ; na. 

 anterior and posterior nares ; P. palatine 

 region of palatoptervgoid ; P. s<ph. para- 

 sphenoid ; Pt. pterygoid ; Qv. quadrate 

 region ; To. vomer. (From Dean, after 

 .Glinther.) 



