SKELETON OF DIPNOI. 



73 



Fig. 35. 



-Palatal view of Skull of 

 Ceratodus. 



Maxillary and intermaxillary elements are not developed, 

 but, perhaps, represented in 

 Ceratodus by some inconstant 

 mdimentary labial cartilages 

 situated behind the posterior 

 nasal opening. Facial cartil- 

 ages and an infraorbital ring 

 are developed at least in Cera- 

 todus, The presence of a pair 

 of small teeth in front indicates 

 the vomerine portion {v) which 

 remains cartilage, whilst the 

 posterior pair of teeth are im- 

 planted in a pterygo-palatine 

 ossification (/), which some- 

 times is paired, sometimes continuous. The base of the skull 

 is constantly covered by a large basal ossification (o). 



The hyoid is well developed, sometimes reduced to a pair 

 of ceratohyals, sometimes with a basihyal and glossyhyal. 

 The skeleton of the branchial a2')paratus approaches the Tele- 

 osteous type, less so in Lejjidosiren than in Ceratodus, in which 

 five branchial arches are developed, but with the lateral and 

 mesial pieces reduced in number. 



A large operculum, and a smaller sub- or inter-operculum 

 are present. 



The scapular arch consists of a single median transverse 

 cartilage, and a pair of lateral cartilages which bear the 

 articular condyle for the pectoral limb. The latter cartilages 

 form the base of a large membrane-bone, and the whole 

 arch is suspended from the skull by means of an osseous 

 supraclavicle. 



The fore-limb of the Dipnoi (Fig. 36) differs externally 

 greatly from the pectoral fin of other Ganoid fishes. It is 

 covered with small scales along the middle, from the root 



