516 BRITISH FOSSIL REPTILES. 



vertebral column, fi'oni the first cervical to the last sacral inclusive, of the length of 3 feet 



2 inches, is 8 inches, including the tarsus ; the length of the fore-foot, including the 

 carpus, in the same skeleton, is 5 inches 4 lines. 



In the skeleton of an Iguana, with the same part of the vertebral column 9 inches 



3 lines in length, the length of the hind-foot, including the tarsus, is 4 inches 5 lines ; 

 that of the fore-foot, including the carpus, being 2 inches 3 lines. 



In most recent ReptUia the fore limbs are shorter than the hind ones ; in some of the 

 tailless Batrachians the difference is extreme. But there is nothing in the proportions 

 or structures, especially in the approach to the ungulate type of the unequal phalanges of 

 the fore-foot of the Iguanodon, to justify, encourage, or even suggest that the fore limbs 

 so terminated did not take their share, as in the Iguanas and Crocodiles, in terrestrial 

 locomotion. 



The notion of the Iguanodon being a biped, and walking like a Ijird, would, were it 

 true, lend countenance to the reptilian hypothesis of the Ornithicnites. 



But this notion would imply, not only ignorance of the structure of the fore limbs of 

 the huge reptile, but also forgetfulness or disregard of the correlated conditions of avian 

 bipedal progression on dry land. 



In proportion to the bulk and weight of the bird, and to its limitation to terrestrial 

 locomotion, is the extent of the trunk-vertebrge grasped by the splints or side bones ('ilia'), 

 which transfer the weight of the body upon the hind limbs. Thus, the ostrich has twenty 

 coalesced sacral vertebras. 



We have no evidence that the Iguanodon had more than four sacral vertebra, and our 

 knowledge of their characters is derived, as might be expected from the remains of a cold- 

 blooded prone quadruped, from detached and unanchylosed sacral centrums. 



Observation of the genesis of the bird's sacrum showed,^ among other points, the 

 alternating disposition of the central and neural elements ; and progressive research into 

 the osteology of the extinct Bejjtilia led to the recognition of a correspondence in this par- 

 ticular of the sacrum of the large Dinosaurs with that of Birds. But this afforded no 

 ground to the Discoverer of the sacral structure for affirming or predicating a closer affinity 

 of the Iguanodon or Megalosaur than of the Pterodactyle to the feathered class. 



In the strong ligament of the head of the femur in Birds — in the dejith of the socket 

 for its reception — in the strength and close adjustment of the knee-joint, in which the 

 fibula takes its share — in the well-turned trochlear form of the distal end of the tibia — in 

 the rejection of any intermediate tarsus between it and the foot, and in the consolidation 

 of the metatarsal bones for a firm and close articulation with the tibia, we may discern 

 a perfect adaptation to the requirements of the single pair of limbs to which the functions 

 of support, station, and progression on land, are exclusively confided. 



' Owen, 'On the Archetype and Homologies of the Vertebrate Skeleton,' 8vo, 1848, p. 1.t9, fig. 27; 

 ' Catalogue of the Osteological Series in the Museum of the Royal College of Surgeons,' 4to, 1853, p. 266. 



