CERATODUS 87 



Characters of Ceratodus which are lacking in other living 

 fish, but present in Amphibia : 



Respiratory lung ; 



Pulmonary arteries and veins ; 



Divided auricle, and conus arteriosus ; 



Vena cava inferior ; 



Anterior abdominal vein ; 



Anterior and posterior nostrils : the latter within the 



mouth ; 

 Autostylic suspension of jaws ; 

 Ascending process ; 

 Cerebral hemispheres. 



Characters of Ceratodus which are primitive when compared 

 with other fish : 



Cloaca ; 



Contractile conus ; 

 Uninterrupted notochord ; 

 Diphycercal tail ? 

 Spiral valve in intestine. 



Characters of Ceratodus which are secondary and specialised : 



Loss of Maxilla and Premaxilla ; 



Median membrane-bones over the skull ; 



Lack of ossification in the cartilaginous neurocranium ; 



Specialised tooth-plates ; 



Fusion of vertebrae on to the back of the skull ; 



Ventral ribs ; 



Rotation of the lung to the dorsal position. 



It will be obvious from these tables that Ceratodus and the 

 Dipnoi generally are very remarkable animals. On the one 

 hand, they have a surprising number of characters which no 

 other fish possess, and which are typical of Amphibia ; yet, 

 on the other hand, their relationship with the Amphibia cannot 

 be very close, because of the large number of specialised 

 characters which they show. 



