242 



DIPNOI 



ail. 



but larger in the early fossils (Figs. 206-7, 225). The jaws of the 

 Dipnoi have undergone profound modification in connection with the 



development of the great compound 

 tooth-plates. Correlated with this 

 are the complete fusion of the pteiy go- 

 quadrate bar in front and behind with 

 the skull, the reduction of the hyo- 

 mandibular and of the marginal teeth 

 and bones of the jaws, and the growth 

 of the splenial and pterygoid bones. 

 It can scarcely be doubted that the 

 Dipnoi have been derived in remote 

 pre- Devonian times from ancestors 

 possessing a more normal palatal 

 dentition, marginal teeth and bones, 

 a detached quadrate, and a hyoman- 

 dibular of moderate size. 



J 



The two halves of the simple 

 ventral view of the palate of Dipterus cartilaginous pectoral girdle fuse 



restored, a.n, anterior nostril ; p, palato- . . * . fe 



pterygoid bone ; pa, parasphenoid ; p.n, in the middle line in CemtoUUS 



posterior nostril ; p.t, palatine tooth : v.t, /-n- mn\ T ^.u- j ii_ 



vomeiine tooth. (Fig. 212). In this and other 



primitive Dipnoi there are paired 

 ventral clavicles overlying the coracoid region, and paired cleithra 



Fio. 210a. 



Upper dentition of a young Ceratodus Forsteri. (After Semon, from Gegenbaur, I'ergl. Anal.) 

 V, vomerine plate ; P, palatine plate. The denticles are joined at their base by a delicate bony 

 network. 



over the scapular region. The cleithrum is connected with the 

 skull by a post-temporal. In the Dipneumones the shoulder-girdle 



