ROOM III. PECTORAL ARCH OF THE IGUANODON. 279 



such as the Ichthyosaurus and Plesioaaurus, of which we have fortunately 

 nearly perfect skeletons, and hence cannot be led astray in the labyrinth 

 of fragments from which we are compelled, in most instances, to con- 

 struct the lost denizens of the former lands and seas of our globe." ! 



PECTORAL ARCH OP THE IGUANODON. In the lacertian 

 reptiles the construction of the pectoral arch is much more 

 complicated than in the Crocodiles. The sternum is a long, 

 narrow, and depressed bone, that gives out two lateral 

 branches, and between which its point sometimes passes and 

 proceeds more in front under the neck. There is also a still 

 greater difference, in the development of the coracoid, and in 

 the constant presence of a clavicle. The coracoid furnishes 

 nearly one half of the glenoid cavity, or socket for the head 

 of the humerus, and gives out one or more apophyses to sup- 

 port a large cartilaginous arch which passes over the narrow 

 bone in front of the sternum, and crosses that of the coracoid 

 on the other side. There is always a foramen for the vessels, 

 pierced in the neck of the bone, between its apophyses and 

 the glenoid facet. The scapula or omoplate forms the other 

 portion of the glenoid cavity ; in the middle, or about one 

 third of its length, the osseous part suddenly terminates, and 

 is continued by a cartilaginous portion : this frequently 

 becomes ossified, and then the scapula is constantly divided 

 into two bones. 2 



The dismembered state in which even the more strongly 

 connected bones of the skeleton occur in the Wealden deposits, 

 rendered it very unlikely that the elements of the pectoral 

 arch should be found in such contiguity as to exhibit the 

 construction of this important part of the fabric ; and it is 

 only within the last three years that I have obtained data by 

 which the restoration of its structure could be attempted. 

 The slender and complicated bone that enters into the com- 

 position of the pectoral arch of the Iguanodon, the Clavicle, 

 was obtained entire before the lamented death of the illustrious 

 Cuvier ; yet this bone, like the teeth, was so anomalous in its 

 characters, as to render its interpretation very difficult. 



CLAVICLE OP THE IGUANODON. Wall-case C, lowest com- 

 partment, (ante, p. 227.) The clavicle in the Iguanas and 



" Philos. Trans.," 1849 ; pp. 293, 294. 

 2 Cuvier's "fiegne Animal" 



