WEALDEN FORMATIONS. 33 



the " head," widens as it sinks, its dilated termination answering to a foramen at that 

 part of the coracoid in the Iguana, Istiurus, and Grammatophora : a smooth rounded 

 notch divides the back part of the head from the backwardly produced obtuse angle of 

 the bone, fig. 2, g. There is no process extended forwards from the fore part of the 

 "body" of the bone: a notch, fig. 1, h, which penetrates the bone at the fore part of 

 scapular end of the bone, as in the Lacertians above named ; the lower and inner 

 border of the expanded body of the coracoid describes a full semi-oval contour, 

 which, in Mr. Holmes's specimen, fig. 2, is broken by a short and narrow notch, 

 entering about the middle of that border. 



In the comparative simplicity of the coracoid of the Iguanodon we may discern an 

 affinity to the Crocodilian reptiles, and in its degree of expansion an affinity to the 

 Lacertian order : this bone, as well as some other part of the skeleton, manifesting the 

 intermediate position of the herbivorous Dinosaur, and its adherence to a more general 

 type of Reptilian organization, than the modern forms of Reptile present. 



An articular portion of the coracoid, measuring 10 inches in diameter, and dis- 

 covered in the Wealden of Tilgate forest, is preserved in the British Museum. 



The chief mark of difference from the Crocodilian structure of the scapular arch, 

 and of resemblance to the Lacertian type, is the presence of a distinct pair of clavicles, 

 the form of which is well shown in the instructive collection of parts of the same 

 skeleton of the Iguana, discovered by Mr. Benstead, in his Green Sand quarry, near 

 Maidstone. The only other bones to which the long and slender ones, marked 

 " clavicle," in Tab. XXXIV, ■ Mon. Cret. Reptiles,' can be compared, are the thoracic 

 ribs and the fibulae. The presence of the fibula in the same block of stone, and its 

 discovery in close proximity with the tibia and femur in the Wealden strata, satisfac- 

 torily prove that the present remarkable bone cannot have formed part of the hinder 

 extremity. And since, in most recent lizards, the radius, which is the more slender 

 of the two bones of the fore-arm, differs from the fibula in little more than in being 

 somewhat shorter and thicker, there is still less reason for supposing the bone in 

 question to have belonged to the fore arm. 



The form of the ribs of the Iguanodon is well known ; their characteristic proximal 

 extremity, in the longer anterior pairs of thoracic ribs, is shown in Tab. II, and they 

 become shorter and more curved as they advance from the middle to the anterior part 

 of the chest. 



Amongst the bones obtained by Dr. Mantell from the quarry-men of Tilgate forest, 

 and submitted by him, in 1830, to the examination of Baron Cuvier, was one, 28 inches 

 in length, now in the British Museum, which the great founder of Palaeontology thought 

 " might be a clavicle:"* portions of other homologous bones have been found, indi- 



* This opinion is cited by Dr. Mantell in his ' Geology of the South-East of England,' 8vo, 1833 

 p. 308. 



