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fragments of the rest of the skeleton, are artificially restored. (Hawkins.)

PLATE 8. V. I. p. 135.

1. Skeleton of a young Ichthyosaurus communis, in the collection of the Geological Society of London, found in the Lias at Lyme Regis. (Scharf. Original.) 2. Ichthyosaurus intermedius, from Lyme Regis, belonging to Sir Astley Cooper. (Scharf. Original.)

PLATE 9. V. I. p. 135.

1 and 2. Ichthyosaurus tenuirostris, from the Lias near Glastonbury, in the collection of the Rev. Dr. Williams, of Bleadon, near Bristol. The position of the ribs is distorted by pressure. (Scharf. Original.) 3. View of the right side of the head of the same animal. (Original.)

PLATE 10. V. I. pp. 135, 137.

1. Head of Ichthyosaurus platyodon, in the British Museum, from the Lias at Lyme Regis, copied from Sir E. Home's figure in the Phil. Trans. 1814. 2. Copied from Mr. Conybeare's figure, (in the Geol. Trans. Lond. O. S. Pl. XL. Fig. 11.) showing the analogies between the bones of the head of Ichthyosaurus, and those which Cuvier has marked by corresponding letters in his figure of the head of the Crocodile.

3. Two of the bony plates in the sclerotic coat of the Eye of Ichthyosaurus platyodon.

4. Circle of bony plates in the Eye of the snowy Owl. (Yarrel.)

5. Circle of similar plates in the Eye of the golden Eagle. (Yarrel.)

6. Front view of bony plates in the Eye of an Iguana. 7. Profile of the same.

8. Two of the fourteen component scales of the same. I owe these three last figures to the kindness of Mr. Allis of York.

A 1, 2, 3, 4. Petrified portions of the skin of a small
Ichthyosaurus, from the Lias of Barrow on Soar,
Leicestershire, presented to the Oxford Museum, by
the Rev. Robert Gutch, of Segrave. (Original.)
In Fig. 1; a, b, c, d, are portions of ribs,

and e, f, g, h, are fragments of sterno-costal bones (nat. size.) The spaces between these bones, are covered with the remains of skin; the Epidermis being represented by a delicate film, and the Rete mucosum by fine threads of white Carbonate of Lime; beneath these the Corium, or true skin, is preserved in the state of dark Carbonate of Lime, charged with black volatile matter, of a bituminous and oily consistence.

2. Magnified representation of the Epidermis and Rete mucosum. The fine superficial lines represent the minute wrinkles of the Epidermis, and the subjacent larger decussating lines, the vascular net-work of the Rete mucosum.

In Fig. 3, the Epidermis exhibits a succession of coarser and more distant folds or wrinkles overlying the mesh-work of the Rete mucosum.

In Fig. 4, the Epidermis has perished, and the texture of the fine vessels of the Reta mucosum is exhibited in strong relief, over the black substance of the subjacent Corium, in the form of a net-work of white threads.*

* Nothing certain has hitherto been known respecting the dermal covering of the Ichthyosauri; it might have been conjectured that these reptiles were incased with horny scales, like Lizards, or that their skin was set with dermal bones, like those on the back of Cro

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PLATE 11. V. I. p. 138.

1. Side View of the head of an Ichthyosaurus, marking

by corresponding letters, the analogies to Cuvier's
figures of the same bones in the head of the Croco-
dile. (Conybeare.)

2. Posterior part of a lower jaw of Ichthyosaurus com-
munis, in the Oxford Museum. (Conybeare.)
3-7. Sections presented by the component bones of Fig.

2 in fractured parts above each section. (Conybeare.) 8. View of the lower Jaw of Ichthyosaurus seen from

codiles; but as the horny scales of Fishes, and dermal bones of Crocodilean animals are preserved in the same Lias with the bones of Ichthyosauri, we may infer that if the latter animals had been furnished with any similar appendages, these would also have been preserved, and long ere this discovered, among the numerous remains that have been so assiduously collected from the Lias. They would certainly have been found in the case of the individual now before us, in which even the Epidermis, and vessels of the Rete Mucosum have escaped destruction.

Similar black patches of petrified skin are not unfrequently found attached to the skeletons of Ichthyosauri from Lyme Regis, but no remains from any other soft parts of the body have yet been noticed.

The preservation of the skin shows that a short interval only elapsed between the death of the animal, and its interment in the muddy sediment of which the Lias is composed.

Among living reptiles, the Betrachians afford an example of an order in which the skin is naked, having neither scales nor dermal bones.

In the case of Lizards and Crocodiles, the scaly, or bony coverings protect the skin from injury by friction against the hard substances with which they are liable to come into contact upon the land; but to the Ichthyosauri which lived exclusively in the sea, there would seem to have been no more need of the protection of scales or dermal bones, than to the naked skin of the Cetacea.

In the case of Plesiosauri also, the non-discovery of the remains of any dermal appendages with the perfect skeletons of animals of that genus, leads to a similar inference, that they too had a naked skin. The same negative argument applies to the flying Reptile Family of Pterodactyles.

beneath, exhibiting the course of its over-lapping bones. (Conybeare.)

A. Tooth of a Crocodile, showing the incipient absorption of the hollow cone which forms its base, from

the effect of pressure of a new tooth rising beneath. (Conybeare.)

B. Similar effects shown in the transverse section of the

upper and lower jaws of an Ichthyosaurus. (Cuvier.) C. Example of the same kind of absorption produced by the pressure of a new tooth, on the base of an older tooth in the jaw of Ichthyosaurus. (Conybeare.)

PLATE 12. V. I. p. 142.

1. Sternal Arch and Paddles of Ichthyosaurus. See V. I. p. 182, Note. (Home.)

2. Sternal Arch of Ornithorhynchus. (Home.)

3, 4, 5, 6. Occipital and Cervical Bones of Ichthyosaurus, from the Lias at Lyme Regis.* (Original.)

* Sir Philip de Malpas Grey Egerton has pointed out some beautiful examples, hitherto unnoticed, in the Atlas and cervical Vertebræ of Ichthyosauri, of peculiar mechanical contrivances to support and regulate the movements of their enormous heads. (See Lond. and Edin. Phil. Mag. Nov. 1835. p. 414.)

Fig. 3, a. represents the Basilar portion of the Occipital bone of a very large and aged Ichthyosaurus, from the Lias of Lyme Regis, (scale one-eighth.) The nearly hemispherical process (a) articulated with a comparatively shallow socket in front of the Atlas, (4. a.) and this ball and socket, or universal joint, gave freedom of motion and support to a weighty head.

Fig. 4. Atlas and Axis of a very young Ichthyosaurus, (two-thirds of nat. size.) These bones adhere together by two nearly flat surfaces, admitting of the least flexure of any of the Vertebræ in the whole body, but giving the greatest strength to that part of the Column, where strength rather than flexure was required.

On the inferior margins of the Atlas and Axis and third cervical vertebra, are triangular facets articulating with three strong wedgeshaped sub-vertebral bones (c) hitherto undescribed.

A. Hollow conical Vertebræ of a fish. (Original.) B. C. E. Vertebræ of Ichthyosaurus. See note, V. I. p. 212. (Home and Conybeare.)

D. a. g. E. a. g. Spinous processes, showing the peculiar articulation of their annular portions, with the Vertebræ, to be adapted to increase the flexibility of the spine. See Note, V. I. p. 134. (Home.)

PLATE 13. V. I. p. 149.

Skeleton of a small Ichthyosaurus, from the Lias at Fig. 4, b. Oblique triangular facet on the lower margin of the front of the Atlas; this facet articulated with the first sub-vertebral wedge, placed between the Atlas and Occiput.

Between the Atlas and Axis, the two sub-vertebral facets formed a triangular cavity for the reception of a second wedge (Fig. 4. c.) and a similar, but smaller cavity received another wedge of the same kind, between the Axis and third Vertebra. This third wedge gave less support to the head, and admitted of more extensive motion than the second. All these three wedge-shaped bones are seen nearly in their natural position in a specimen from Lyme Regis, in the Collection of Sir P. G. Egerton.

Fig. 4. First sub-vertebral wedge, auxiliary to the anterior cavity of the Atlas, in completing the articulating socket for the basilar process of the Occiput (3. a.)

4. a. Crescent-shaped front of the first sub-vertebral wedge.

4'. b. Head of the same Wedge.

4. c. Obtuse apex of the same, articulating with the triangular frontal facet of the Atlas (4. b.) In young animals this frontal facet is nearly smooth and flat; in older animals (3. b′.) it is rugged and furrowed. This articulation must have given to the first sub-vertebral wedge great power as a stay or prop, to resist the downward pressure of the head, at the same time facilitating the rotatory movements of the Occipital bone.

Fig. 4. c. Second sub-vertebral wedge articulating with the triangular cavity formed by the marginal facets of the Atlas and Axis. This second Wedge acted as a strong prop supporting firmly the lower portion of the Atlas, and at the same time admitting the small amount of motion here required.

c'. Head of the sub-vertebral wedge (c) strengthened by a projecting boss of solid bone.

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