32 FOSSIL REPTILIA OP THE 



Bones of the Extremities of the Iguanodon. 



These are remarkable for their superior development in proportion to the vertebrae 

 of the trunk, as compared with, the Iguana, the Crocodiles, and other existing Sauria. 

 The scapular arch accords with the Lacertian type in being complicated with clavicles, 

 and in the great breadth of the coracoid ; but the scapula, in its length and simplicity, 

 resembles more that of the Crocodiles than of the Lizards. 



Scapula, Coracoid, and Humerus. Tab. XIV. One third the nat. size. 



The scapula, PI. XIV, figs. 1 and 2, is a long, flat, narrow bone, slightly bent 

 backwards, gradually contracting in breadth and augmenting in thickness from its free 

 extremity, answering to the base, a, to its articulated end, d, which suddenly expands 

 and developes processes, b, c, before joining the coracoid, /. 



These processes are two in number ; one, b, is from the anterior border a little 

 above the surface, d, for articulation with the coracoid ; it is short and obtuse : the 

 other, e , is still shorter, and comes off from the posterior border just above the articular 

 surface, c, for the head of the humerus. The outer surface of the bone is slightly 

 depressed between these processes, and becomes contracted beneath them where it 

 forms the two articular surfaces, d, c, above mentioned. 



The process, b, answers to the stronger and broader anterior process of the scapula 

 of the Crocodile : the posterior process, <?, seems to have no homologue in the modern 

 Reptilia. 



The scapula in the Amboina lizard, called Istiurus, sends backwards and upwards a 

 process, but it is relatively longer than in the Iguanodon, and comes off higher up the 

 scapula: the Psammosaurus and Grammatophora have no such process, and the entire 

 scapula is much broader in proportion to its length. The scapula of the Iguanodon in 

 general shape resembles that of the Crocodilia more than that of the Lacertian, but it 

 is longer and more slender than in the Crocodile. The scapula, seen fractured across 

 the femur in the Maidstone Iguanodon, see Tab. XXXIV, ' Monogr. Cretaceous 

 Reptiles,' and figured in Dr. Mantell's Memoir, ' Phil. Trans.,' 1841, PI. VIII, fig. 30, as 

 an undetermined bone, repeats all the essential characters of the scapula so beautifully 

 exposed, in natural connexion with the coracoid, in Mr. Holmes's specimen, figured in 

 Tab. XIV, fig. 1. 



The coracoid, fig. 2, /, more closely accords with the Lacertian type of that 

 bone : it is a sub-semioval plate, broader than it is long, with the middle of its straighter 

 border produced and thickened, and divided into two articular facets; one, fig. 1, /, 

 for the scapula, the other, g, for the humerus : this articular part or " head " of the 

 coracoid is marked off by a short constriction or " neck" from the broad plate or 



