700 



PROF. OWEN ON THE RANK AND AFFINITIES IN 



§ 7. The Mandible.— In the lower jaw of Lacertians (fig. 20) 

 may be noted the following pieces in each ramus : — 32, dentary ; 

 33, splenial ; si', coronoid ; 29, articular ; 30, angular ; 31, surangular. 



What is first noticeable in the connexions of these bones, in a com- 

 parison of Lacertians on the one hand with Crocodilia and Chelonia, 

 and with Ophidia on the other hand, is the greater tendency in certain 

 sutures to mark off an anterior half of the ramus, including the 

 dentary, and splenial, from the posterior half; with this modi- 

 fication, that in the Iguanians (fig. 19) the coronoid piece, si', would 

 go with the anterior division, and in the Monitors (fig. 20) with 

 the posterior one. 



The subvertical suture in Amblyrhynchus (fig. 19, s-s) runs from 

 above downward, first between the surangular, 31, and coronoid, 31' ; 

 then between the surangular and the combined splenial 33, and 

 dentary, 32. 



In the Monitor ( Varanus niloticus) (fig. 20) the subvertical suture, 

 s-s, runs, first between the surangular, 31, and the dentary, 32 ; then 

 between the angular, 30, and the combined dentary and splenial. 

 A small part of the fore end of the coronoid, 31', supplements the 

 upper end of this subvertical suture. 



In the Mosasaurus (fig. 18) this subvertical division, s s, of the 



Fig. 18. 



Mosasaurus. 



ramus follows more closely the pattern of the Monitor than of the 

 Iguanians. The chief modification is the formation of the lower 

 part of the suture by the angular, 30, and splenial, 33, exclusive of 



