HADHOSAURUS. 93 



the condyles. Posteriorly the latter are separated by a deep, wide notch. A deep 

 popliteal concavity (Fig. 4, g) communicates below with a short, wide canal (Fig. 

 6, g) perforating the conjunction of the condyles posteriorly. A similar perforation 

 exists in the recent Cyclura. 



The posterior projection of the outer condyle is broken off in the specimen; that 

 of the inner condyle exhibits a large rugged surface (Fig. 4, d) for the gastrocnemial 

 attachment. The external condyle projects rather more inferiorly than the internal, 

 but appears not to have been so extensive in its antero-posterior diameter. 



The interior of the bone exhibits a capacious medullary cavity. 



The measurements of the bone are as foUows: — 



Inches. Lines. 



Length of the femur from top of trochanter to bottom of external 



condyle 41 6 



Length from top of head to bottom of internal condyle . . .39 



Breadth of upper extremity 9 3 



Breadth of lower extremity 8 5 



Transverse diameter at middle of shaft ...... 5 2 



Antero-posterior diameter at middle of shaft ..... 4 6 



Circumference below middle trochanteroid process . . . .15 



Circumference above middle trochanteroid process . . . .It 



Antero-posterior diameter of head 5 8 



Antero-posterior diameter of trochanter ......% 9 



Antero-posterior diameter of inner condyle ..... 10 



In comparing the femur of Hadrosaurus with that of the living Cyclura and 

 Iguana, to which it bears a nearer resemblance than to that of the Crocodiles, it 

 would appear as if the condition of most of the anatomical characters were either 

 reversed or their meaning had been mistaken. Thus in Hadrosaurus we have 

 described the head of the femur as being internal and the trochanter external. In 

 Cyclura and Iguana the head of the bone is external and the trochanter postero- 

 internal. In Hadrosaurus the head is slightly below the level of the trochanter ; 

 in Cyclura it is considerably higher. In Hadrosaurus the shape of the trochanter 

 is nearly like that of the head in Cyclura, and is nearly as large as the head of the 

 same bone, but in Cyclura it is much smaller. In the former the femur is longest 

 from the trochanter to the external condyle ; in the latter from the head to the 

 external condyle. Lastly, in Hadrosaurus the internal condyle is the larger ; in 

 Cyclura the external is the larger. 



The tibia of Hadrosaurus, represented in Figs. 1-6, Plate XVI, is of the left 

 side. It approaches in form and details of structure that of the Iguanodon, as 

 represented in Prof. Owen's Fig. 2, Plate XX, of the British Fossil Eeptiles, Dino- 

 sauria. It is, however, proportionately more slender towards the middle of the 

 shaft, and it appears twisted in such a manner that the broad extremities cross 

 each other in the direction of their greatest diameter, whereas in Iguanodon the 

 broad extremities are nearly on the same plane. 



The tibia is about three feet in length, and is cylindroid at the middle of the 

 shaft, which rapidly expands into broad, clavate extremities. 



The fore part of the shaft. Fig. 1, is nearly straight vertically, is smooth, and 

 widest at its upper part. For the greater part of its extent it is transversely con- 



