46 pkof. owen on some dinosaueian veetebe^e. 



Discussion. 



Prof. Seeley wished to ask the author whether other specimens 

 gave a better idea of these Dinosaurs. He thought that the Dino- 

 sauria and the Dicynodonts, in the structure of the pelvis and of the 

 fore and hind limbs, resembled each other much more closely than 

 any other two orders. He inquired whether this evidence did not 

 break down the classifieational value of the Dinosauria. The aper- 

 tures seemed to him to be equivalent to the hollows in the vertebras 

 of birds, which are connected with the extension of the respiratory 

 system throughout the body ; and thus, as they occur in Dinosaurs 

 and in Pterodactyles, they seem to aid in breaking down the de- 

 markation between these groups. He also thought that he had 

 observed the same structure in Dicynodonts. The specimens de- 

 scribed by Prof. Owen appeared to him to open up some very broad 

 philosophical questions. 



Prof. Owen said :— "The 'Philosophical Transactions ' (1862), it 

 is true, show that a Dicynodont had a sacrum of several vertebrae, 

 as in the Dinosaurs. The structure of the hind limbs of Dicynodonts 

 is not known ; but that of the fore limbs shows a humerus perforated 

 above the inner condyle, and three-jointed digits, save the pollex, 

 which has two joints, in their pentadactyle fore paw. Besides this 

 difference from Dinosaurs, the premaxillaries are confluent as one 

 bone, with an edentulous trenchant border, evident .y, like the cor- 

 responding border of the edentulous lower jaw, sheathed with a 

 beak-like substance. The Dicynodonts in their pair of long upper 

 tusks, and the Oudcnodonts in their toothless jaws, further differ 

 from Dinosaurs ; and both agree in having vertebras cupped as in 

 Ichthyosaurus, a character which no Dinosaur of Liassic and later age 

 presents. The ordinal terms Dinosauria, Anomodontia, Pterosauria, 

 Crocodilia, so long as they are oxpressive of distinctive characters of 

 the groups of Reptilia so associated, are useful instruments in gaining 

 farther knowledge of the class. To extend any one of those terms 

 to another group which may have a single character, added to those 

 of class, in common with another, is to cast away the advantage of 

 an ordinal term significant of actual knowledge of a sum of charac- 

 ters." He added that no Dicynodont, Oudenodont, or Endothiodont 

 species of the order Anomodontia has hitherto been found in strata 

 unquestionably so recent as those that have yielded species of Dino- 

 sauria, other than Ketospondylian. 



