[587] In Crocodiles the abdominal region is strengthened by slender ribs (hæmapophyses, Prof. Owen), that are affixed to a ligamentous extension of the cartilaginous sternum, analogous to the linea alba in man; and the Hylæosaurus appears to have possessed a similar development of the costal elements, for I observed many fragments of long, slender, sub-cylindrical rib-like bones whilst chiselling off the stone from this species, and portions of similar bones occur in the stone around the spinal column from Bolney. In the Maidstone Iguanodon there are likewise some long slender bones of this character, which I think must be prolongations of the ordinary dorsal ribs.

Extremities.—The locomotive extremities are variously constructed, according to the adaptation of the animals to a terrestrial, fluviatile, or marine existence. The bones of the limbs in the extinct colossal terrestrial species much resemble those of our large pachydermata, the Rhinoceros and Hippopotamus. The cylindrical bones of the extremities in the Crocodilians, and other recent reptiles, are solid. i. e. have no cavity filled with marrow; such also is the case in the fossil Enaliosaurians; but the thigh-bones and leg-bones of the Iguanodon, and of other extinct land saurians, h ave a large medullary canal. Our limits will not admit of further osteological details; and we are compelled to omit the description of the bones composing the thoracic and pelvic arches.

Dermal Bones. Ligns. [207] and [208]. In many of the reptile tribes, particularly of the Crocodilian or loricated (mailed) group, there are immediately under the external integument or skin a series of osseous scutes, or scutcheons, variously arranged, which serve as supports to the integumental scales and spines. In the gigantic Gavial, that inhabits the Ganges and other rivers of India, and which is remarkably distinguished from the common Crocodile and Alligator by an extremely elongated slender muzzle, the nape of the neck is protected by sixteen or eighteen transverse rows of dermal scutes; and there are likewise six rows which extend down the back. These bones are deeply corrugated or sculptured on their upper surface; a structure adapted for the firm adhesion of the horny integument.

Detached bones of this character occur in the Purbeck strata; and the first fragments I collected were supposed by me to belong to the soft-skinned turtles (Trionyces); but the subsequent discovery of perfect scutes demonstrated their analogy to the dermal bones of the Gavial, and enabled me to determine their true character.

Lign. 207. Dermal Bone of the Swanage Crocodile: 1/3 nat.
Purbeck.
(Goniopholis crassidens.)

Fig.1.—The external aspect.
2.—The inner surface.
a.—The lateral connecting process.

In the splendid specimen of the fossil remains of a Crocodilian reptile (Goniopholis), found at Swanage (Wond. pp. 415; and Petrif. p. 170), there are numerous dermal examples dispersed among the bones, as shown in Petrif. Lign.