124 THE VERTEBRATE SKELETON. 



The skull of TELEOSTEI is very similar to those of Lepidosteus 

 and Amia. Although the bony skull is greatly developed and 

 very complicated, much of the original cartilaginous cranium 

 often persists. Membrane bones are specially developed on 

 the roof of the skull where they include the parietal, frontal, 

 and nasal bones. The same bones are developed in connection 

 with the upper jaw and roof of the mouth as in bony Ganoids, 

 but only two membrane bones occur in the lower jaw, viz. the 

 angular and' dentary. A number of large ossifications take 

 place in the cartilage of the auditory capsules. In some forms 

 parts of the last pair of branchial arches are broadened out 

 and form the pharyngeal bones which bear teeth. The oper- 

 cular bones and those of the upper and lower jaws are quite 

 comparable to those of bony Ganoids. 



A full account of the Teleostean skull has been given in 

 the case of the Salmon (pp. 87 96) and the Cod (pp. 96 

 101). 



In DIPNOI the skull is mainly cartilaginous, but both 

 cartilage- and membrane-bone occur also. Cartilage-bone is 

 found in the ossified exoccipitals, while of membrane-bones 

 Protopterus has among unpaired bones a fronto-parietal, a 

 median ethmoid, and a parasphenoid, and among paired bones 

 nasals and large supra-orbitals. The skull of Ceratodus (fig. 19) 

 has an almost complete roof of membrane bones, including some 

 whose homology is doubtful. The ethmo-vomerine region is 

 always cartilaginous, but bears small teeth. The palato- 

 pterygo-quadrate bar is ossified and firmly united to the 

 cranium, and the mandible articulates directly with it (auto- 

 stylic). Membrane bones are freely developed in connection 

 with the mandible, dentary, splenial, and angular bones being 

 all present. There are two opercular bones. 



In the extinct Dipteridae the cranium is very completely 

 covered with plates of dermal bone, and the skeleton in 

 general is more ossified than is the case in recent Dipnoi. 



Six pairs of branchial arches occur in Protopterus ; Cera- 



