WEALDEN FORMATIONS. 25 



alveolar parapet, and to rapidly worn and renewed horny scales covering the outside 

 of the rami of the lower jaw. The like differences of the condition of the soft parts 

 external to the upper jaw govern corresponding modifications of the nervo-vascular 

 foramina of the bones of that part. It will be obvious, on the slightest reflection, that 

 the horny scales or scutes covering the borders of the jaws in reptiles must be those 

 that are subject to most abrasion, moistening, and other influences accelerating their 

 decay ; and in the living Saurians it may be generally seen that the marginal scales or 

 scutes of the jaws exhibit the effects of such destructive influences contingent on their 

 position. As these scales are more quickly worn away than those of other parts, so 

 they are more rapidly renewed ; their progress of growth is quicker, and their formative 

 beds in the cutis have a greater supply of both vessels and nerves : the greater 

 vascularity of this part of the integument is shown by injecting the head of a 

 crocodile or lizard, and macerating away the cuticular scales. The labial muco- 

 salivary follicles are arranged commonly in a linear series, and their orifices may be 

 seen in a row along the narrow and shallow groove between the alveolar border and 

 the scaly integument forming the margin of the mouth : these follicles, in most 

 Saurians, perform the offices assigned to the more compact and localized salivary 

 glands in Mammalia ; and consequently require and exhaust a good supply of blood. 

 The arteries emerging from the serial foramina resolve themselves each into a brush of 

 small branches which are spent in the vascular matrices of the labial scales and on the 

 secreting surfaces of the labial glands. 



In the great Mosasaurus, as is shown in PI. XVIII, of the ' Ossemens Fossiles,' 

 of Cuvier,* the linear series of nervo-vascular foramina along the outside of 

 the ramus of the lower jaw indicates plainly that such jaw was covered by a firm scaly 

 integument protecting a long series of muco-salivary follicles, as in existing Saurians. 

 In the great Megatherium and Mylodon the single or double large nervo-vascular 

 outlets confined to the fore part of the mandibular rami equally attest the existence of 

 fleshy and sensitive lips produced beyond the fore part of the jaw, and capable of being 

 further protruded and retracted. 



It needs only a comparison of the lower jaw of the Iguanodon with that of the 

 Mosasaurus and of any recent reptile, and with that of the Megatherium and of any 

 recent Mammal, to arrive at a correct conclusion as to whether the Iguanodon 

 resembled the Saurians in the covering of its jaws, or presented the monstrous 

 combination of mammalian lips with a reptilian skeleton. 



I have only to add that the form of the anterior termination of the jaw of the 

 Iguanodon is diametrically opposite to that of the Mylodon : in the former, the upper 

 border slopes downwards and forwards at an angle of 45° to the straight inferior 

 border; in the latter the inferior border bends upwards and forwards at nearly the 

 same angle to the straight upper border. In the reduced figure of the lower jaw of 



* Ed. 4to, 1824, torn, v, pt. 2. 



4 



