ON BRITISH FOSSIL REPTILES. 135 



In. Lin. 



The breadth of the expanded sternal end of'a clavicle, 29 1 „ ,. 



inches in length, is J 



The breadth of the scapular end 4 3 



From this extremity to the base of the first process . . .19 

 The breadth of the narrowest part of the shaft .... 1 7 



Humerus. — This important bone has not been hitherto satisfactorily deter- 

 mined ; it differs less from the femur in form in Reptiles than in Mammalia. 

 In the Crocodilians it is shorter than the femur, especially in the extinct pis- 

 civorous species, with biconcave vertebrae and more strictly aquatic habits. 

 In Lizards it is more nearly equal with the femur, and the similarity of the 

 size of these bones we may conceive to have been greater in the gigantic ter- 

 restrial Dinosaurs. 



In the modern Crocodiles, the chief distinction in the form of the humerus 

 is the ridge at the upper third of the bone : in Lizards this distinction is 

 almost lost. If we find the femur of the Iguanodon distinguished from that 

 of all other reptiles by the presence of a peculiar process from the inner side 

 of the bone, there are not wanting grounds to expect that the humerus may 

 present a similar character. 



As the reasons for suspecting that some of the large bones, hitherto uni- 

 formly regarded as the femora, may be the humeri of the Iguanodon, will best 

 appear in the description of the femur, I shall now proceed to the considera- 

 tion of the large bones with which the femur is articulated. 



Ilium.— The iliac bone o{ the IgjMnodo7i* resembles in form that of the Mo- 

 nitor more than that of the Iguana : in the portion of the pelvis in Mr. SauU's 

 collection it measured 14 inches in length. It commences anteriorly by a 

 thick obtuse extremity slightly bent outwards ; this part is supported by the 

 thickest and strongest of the sacral ribs, which slightly inclines backwards : 

 the ilium quickly increases in vertical as well as transverse extent, forming at 

 its lower part the usual portion of the acetabulum ; the concavity terminating 

 behind in a broad obtuse prominence : behind this part the ilium rapidly con- 

 tracts, by a deep inferior emargination, to a comparatively slender process ex- 

 tending backwards and gradually diminishing to an obtuse point, well shown 

 in the detached ilia of the Maidstone Iguanodon, but here broken off. The 

 chord of the acetabular arc or concavity, in Mr. SauU's specimen, measured 

 8 inches. 



In the Maidstone Iguanodon the left ilium lies detached, with its sym- 

 physial articulation or inner surface uppermost, indicating by the extent of 

 that surface, which equals the antero-posterior diameter of nearly five of the 

 dorsal vertebraj of the same individual, the length of the sacrum peculiar to 

 this and other Dinosaurian reptiles. Its slender posterior portion terminates 

 in a subacute point : the anterior extremity of the right ischium, which has 

 the opposite surface exposed, bends slightly outwards in the form of a thick 

 tuberosity. In. Lin. 



The length of this bone is 16 



Its depth 5 



From the anterior tuberosity to the posterior angle 1 g q 

 of the acetabulum J 



Pubis This bone, which presents a simple spatulate form in the Croco- 

 diles, already begins to increase in breadth at its symphysial extremity in the 

 extinct family with concave vertebra ; and in the larger existing species of 

 Lizards is expanded at both extremities, and has a very marked and recog- 



* This bone is figured in Dr. ManteU's Memoir, Phil. Trans. 1841, pi. viii. fig. 28. 



