than those we have been examining in the case of the Pterodactyle. We find the details of parts which, from their minuteness should seem insignificant, acquiring great importance in such an investigation as we are now conducting; they show not less distinctly, than the colossal limbs of the most gigantic quadrupeds, a numerical coincidence, and a concurrence of proportions, which it seems impossible to refer to the effect of accident; and which point out unity of purpose, and deliberate design, in some intelligent First Cause, from which they were all derived. We have seen that whilst all the laws of existing organization in the order of Lizards, are rigidly maintained in the Pterodactyles; still, as Lizards modified to move like birds and Bats in the air, they received, in each part of their frame, a perfect adaptation to their state. We have dwelt more at length on the minutiae of their mechanism, because they convey us back into ages so exceedingly remote, and show that even in those distant eras, the same care of a common Creator, which we witness in the mechanism of our own bodies, and those of the myriads of inferior creatures that move around us, was extended to the structure of creatures, that at first sight seem made up only of monstrosities.

SECTION IX.

MEGALOSAURUS.*

THE Megalosaurus, as its name implies, was a Lizard, of great size, of which, although no skeleton has yet been found entire, so many perfect bones and teeth have been discovered in the same quarries, that we are nearly as well acquainted with the form and dimensions of its limbs, as if they had been found together in a single block of stone.*

From the size and proportions of these bones, as compared with existing Lizards, Cuvier concludes the Megalosaurus to have been an enormous reptile, measuring from forty to fifty feet in length, and partaking of the structure of the Crocodile and the Monitor.

This genus was established by the Author, in a Memoir, published in the Geol. Trans. of London, (Vol. I., N. S. Pt. 2, 1824), and was founded upon specimens discovered in the oolitic slate of Stonesfield, near Oxford, the place in which these bones have as yet chiefly occurred. Mr. Mantell has discovered remains of the same animal in the Wealden fresh-water formation of Tilgate Forest; and from this circumstance we infer that it existed during the deposition of the entire series of oolitic strata. The author, in 1826, saw fragments of a jaw, containing teeth, and of some other bones of Megalosaurus, in the museum at Besançon, from the oolite of that neighbourhood.

As the femur and tibia measure nearly three feet each, the entire hind leg must have attained a length of nearly two yards: a metatarsal bone, thirteen inches long, indicates a corresponding length in the foot.* The bones of the thigh and leg are not solid at the centre, as in Crocodiles, and other aquatic quadrupeds, but have large medullary cavities, like the bones of terrestrial animals. We learn from this circumstance, added to the character of the foot, that the Megalosaurus lived chiefly upon the land.

In the internal condition of these fossil bones, we see the same adaptation of the skeleton to its proper element, which now distinguishes the bones of terrestrial, from those of aquatic Saurians. In the Ichthyosauri and Plesiosauri, whose paddles were calculated exclusively to move in water, even the largest bones of the arms and legs were solid throughout. Their weight would in no way have embarrassed their action in the fluid medium they inhabited ; but in the huge Megalosaurus, and still more gigantic Iguanodon, which are shown by the character of their feet to have been fitted to move on land, the larger bones of the legs were diminished

* See Geol. Trans. 2nd series, Vol. 3, p. 427, Pl. 41.

+ I learn from Mr. Owen that the long bones of land Tortoises have a close cancellous internal structure, but not a medullary cavity.

in weight, by being internally hollow, and having their cavities filled with the light material of marrow, while their cylindrical form tended also to combine this lightness with strength.*

The form of the teeth shows the Megalo

* The medullary cavities in the fossil bones of Megalosaurus, from Stonesfield, are usually filled with calcareous spar. In the Oxford Museum there is a specimen from the Wealden freshwater formation at Langton, near Tunbridge Wells, which is perhaps unique amongst organic remains: it presents the curious fact of a perfect cast of the interior of a large bone, apparently the femur of a Megalosaurus, exhibiting the exact form and ramifications of the marrow, whilst the bone itself has entirely perished. The substance of this cast is fine sand, cemented by oxide of iron, and its form distinctly represents all the minute reticulations, with which the marrow filled the intercolumniations of the cancelli, near the extremity of the bone. It exhibits also casts of the perforations along the internal parietes, whereby the vessels entered obliquely from the exterior of the bone, to communicate with the marrow. A mould of the exterior of the same bone has been also formed by the sandstone in which it was imbedded: hence, although the bone itself has perished, we have precise representations both of its external form and internal cavities, and a model of the marrow that filled this femur, nearly as perfect as could be made by pouring wax into an empty marrow-bone, and corroding away the bone with acid. The sand which formed this cast must have entered the medullary cavity by a fracture across the other extremity of the bone, which was wanting in the specimen.

From this natural preparation of ancient anatomy we learn that the disposition of marrow, and its connection with the reticulated extremities of the interior of the femur, were the same in these gigantic Lizards of a former world, as in medullary cavities of existing species.

saurus to have been in a high degree carnivorous it probably fed on smaller reptiles, such as Crocodiles and Tortoises, whose remains abound in the same strata with its bones. It may also have taken to the water in pursuit of Plesiosauri and fishes.*

The most important part of the Megalosaurus yet found, consists of a fragment of the lower jaw, containing many teeth, (Pl. 23, Figs. 1-2). The form of this jaw shows that the head was terminated by a straight and narrow snout, compressed laterally like that of the Delphinus Gangeticus.

As in all animals, the jaws and teeth form the most characteristic parts, I shall limit my present observations to a few striking circumstances in the dentition of the Megalosaurus. From these we learn that the animal was a reptile, closely allied to some of our modern Lizards; and viewing the teeth as instruments for providing food to a carnivorous creature of enormous magnitude, they appear to have been admirably adapted to the destructive office for which they were designed. Their form and

* Mr. Broderip informs me that a living Iguana (I. Tuberculata), in the gardens of the Zoological Society of London, in the summer of 1834, was observed frequently to enter the water, and swim across a small pond, using its long tail as the instrument of progression, and keeping its fore feet motionless.