One of these is figured [Lign. 207]; fig. 1 represents the external surface, which is deeply sculptured by irregular roundish pits or excavations; the under or inner surface, fig. 2, is smooth, but marked with very fine striæ, decussating each other at right angles, as in the dermal bones of the Hylæosaurus ([Lign. 208], fig. 1a.). These scutes differ from those of other recent and fossil Crocodilians, in a lateral conical projection, marked a, figs. 1, 2, [Lign. 207], which fits into a depression on the under surface of the opposite angle of the adjoining plate; resembling, in this respect, the scales of the Lepidotus (see [Lign. 196], p. 605). Numerous hexagonal and pentagonal scutes, articulated together by marginal sutures, also entered into the composition of the osseous dermal cuirass of this reptile, which must, therefore, have possessed a flexible, yet impenetrable, coat of armour, capable of affording protection against the attack of any assailant.
In the Oolite, the dermal bones of other slender-nosed Crocodilians (Teleosaurus) are occasionally met with; the outer surfaces of which are marked with small circular distinct pits; these scutes are thicker and more rectangular than those above described, and slightly overlapped each other laterally; they have no connecting process. In another species one half of the outer surface is smooth, proving that it was covered to that extent by the adjoining scute.[588]
[588] A description of the dermal bones of British fossil reptiles is given in Brit. Assoc. Report for 1841, pp. 70, 79, &c.
Dermal Bones of the Hylæosaurus.—Elliptical and circular dermal scutes, having the under surface flat and the upper convex with a conical tubercle, were first noticed in the specimen of the Hylæosaurus, figured Wond. pl. iv.; and I have since discovered similar bones associated with other remains of that extraordinary reptile; reduced figures of two specimens are represented in [Lign. 208], figs. 1, 3.
Lign. 208. Dermal Bones of Reptiles. Tilgate Forest.
| Fig. | 1, and 3.— | Dermal bones of the Hylæosaurus: 1/3 nat. |
| 1a.— | The under surface of a fragment of a dermal bone, displaying fine spicula, decussating each other at right angles, and indicating a similar structure to that of the Curium, in which the bones were imbedded: nat. | |
| 1b.— | A portion of the same, highly magnified, and viewed by transmitted light. | |
| 2.— | Horn of Iguanodon: 1/6 nat. | |
| 4.— | A Dorsal Spine of the Hylæosaurus; the original is thirteen inches long. |
The structure of these bodies is very remarkable; upon closely inspecting the under side, and the surface exposed by a transverse fracture, very minute osseous spicula, decussating each other at right angles, are distinctly seen; as shown in [Lign. 208], fig. 1a. In fig. 1b, a thin slice of the same, highly magnified, and viewed by transmitted light, displays medullary canals, with very fine lines radiating from them. The peculiar character of this organization consists in the disposition of the straight bony spicula; an appearance which first attracted my attention when developing the original specimen of the Hylæosaurus (see Geol. S. E. p. 327), and led to the discovery of some perfect examples, which otherwise would have been destroyed. This structure closely resembles that presented by the ligamentous fibres of the corium, or skin, and seems to have resulted from an ossified condition of the dermal integument. These bones vary from half an inch to three or four inches in diameter, and were disposed in one or more longitudinal series on each side the spine, diminishing in size as they approach the end of the tail.