310 PETKIFACTIONS AND THEIR TEACHINGS. CHAP. III. 



it is in this order of Mammalia that we find the nearest 

 approach to the Reptilia : in the scaly covering of the skin, 

 the imperfections of the dental system, the smallness of the 

 brain, and the long continuance of the irritability of the 

 muscular fibre after death ; which are so many decadencies 

 of organization, so to speak, that indicate a step towards that 

 class, of which the Iguanodon appears to have been the 

 highest type. 



If the opinion previously advanced (ante, p. 260) be correct, 

 that the anterior part of the spinal column consisted of con- 

 vexo-concave, and the dorsal of plano-concave vertebrae, the 

 adult Iguanodon must have approached in this part of its 

 skeleton, as well as in its sacrum, in its massive femora, 

 with their large medullary cavities, trochanters, and con- 

 dyles, and in its short and strong metatarsals and pha- 

 langeals, to that of the large herbivorous mammalia. 



The position of the hinder limbs (the thighs and legs) in 

 relation to the pelvis, cannot be accurately determined from 

 the data at present obtained; but the form of the head and 

 shaft of the femur, and the character of its articulations and 

 processes, so closely resemble those of the largest pachyderms, 

 as to suggest the idea, that unlike the rest of its class, the 

 Iguanodon had the body supported as in the mammalia, and 

 the abdomen suspended higher from the ground than in any 

 existing saurians. 



In fine, we have in the Iguanodon the type of the terres- 

 trial herbivora, which in that remote epoch of the earth's 

 physical history, termed by geologists " The Age of Reptiles," 

 occupied the same relative station in the scale of being, and 

 fulfilled the same general purposes in the economy of nature, 

 as the Mastodons, Mammoths, and Mylodons, of the tertiary 

 periods, and the existing Pachyderms. 



With regard to the probable magnitude of the individuals 

 to which the largest bones in my collection belonged, a gene- 

 ral estimate only can be formed, because the relative propor- 

 tions of the limbs, head, and body, are still unknown ; sooner 

 or later an entire, or a considerable portion of the, skeleton 

 of a young Iguanodon will be brought to light, and yield the 

 information necessary to enable the palaeontologist to ascertain 

 .the dimensions, and delineate the physiognomy, of the living 

 original. 



