364 PROFESSOR OWEN, ON THE RHYNCHOSAURUS. 



ture as that of the jaw in the cranium above described : the thick 

 edentulous alveolar border is bounded below on the outside by the 

 longitudinal channel : the lower border of the ramus is thick and 

 smoothly rounded, it is somewhat abruptly constricted immediately 

 behind the deflected extremity or symphysis. The structure of the 

 bone is very compact ; the fractured end demonstrates the large cavity, 

 common in Reptiles, which is included between the opercular and den- 

 tary pieces. 



One piece of fine-grained sandstone contains a considerable proportion 

 of four of the dorsal vertebrae in a connected chain, which measures 

 1 inch 10 lines. 



Near this chain of four and a smaller part of a fifth vertebra? 

 there are portions of four ribs. These have a simple, not a bifurcated 

 head ; they are subcompressed, pretty uniformly curved, and grooved 

 longitudinally on both sides ; the longest portion of rib measures two 

 inches, following the curvature. 



The same fragment of sandstone contains three flat bones, which 

 offer several striking modifications, whether they be compared with the 

 constituents of an os innominatum or of the scapular arch. The most 

 entire of the three bones* has a thick articular end, a long, broad, 

 and thin plate, forming the body of the bone ; and a moderately long 

 trihedral process given off from the convex margin near the articular 

 end. In these characters the comparative anatomist conversant with the 

 modifications of the skeleton in recent and extinct Saurians will recog- 

 nise a resemblance to the scapula of the Iguanodon and Hylaeosaur, in 

 a minor degree to the ischium of the Crocodile, and somewhat more 

 remotely to the pubis of the Tortoise. The trihedral process, in the 

 second comparison, would match the anterior pubic process of the Cro- 

 codile's ischium, but the entire bone would differ from that of the 

 Crocodile in the slenderness of the pubic process, in the greater breadth 

 and less length of the body of the bone, and in its extreme thinness ; 

 it increases in thickness, however, as in the Crocodile's ischium, to- 

 wards the articular end. The correspondence of the trihedral process 



* Plate vi, fig. 8. 



