of the Ichthyosaurus. 201 



webbed foot of the Crocodile, but differing in the absence of subdivision by second- 

 ary longitudinal impressions. 



The known structure of the skeleton of the Ichthyosaurus admits of no doubt as 

 to its being essentially an air-breathing, cold-blooded vertebrate animal, and con- 

 sequently a reptile ; the scutiform character of the integument covering the fin is 

 therefore in harmony with the osseous structure. It might have been expected, 

 a priori, that the skin, which, with its appendages, gives a character to the great 

 primary groups of Vertebrata, and, as it were, reflects with more or less clearness 

 their internal organization, should, in the extinct reptiles of the sea, exhibit some 

 of the characters of the integument of existing reptiles*. 



The other new facts which the present most interesting specimen has brought to 

 light, equally accord with the indications of the natural affinities of the Ichthyosauri 

 afforded by its more enduring remains. All the deviations from the Reptilian 

 structure of the skeleton tend to the type of Fishes, and not to that of the Cetaceous 

 Mammalia ; this tendency has always been recognized in the well-known bicon- 

 cave structure of the vertebrae ; but in addition to this Ichthyic structure, the great 

 number and the bifurcation of the digital bony rays of the fins, the great develop- 

 ment of the cervical ribs, the enormous size of the intermaxillary bones, which sup- 

 port nearly the whole of the teeth of the upper jaw, the filling up of the cavities 

 of the conical teeth by a coarse ossification of the remaining dental pulp, and the 

 large size of the orbits and eyes, — all these particulars bespeak the close approach 

 of the Ichthyosauri to the class of Fishes, and prepare us to receive with less sur- 

 prise the evidence of a Malacopterygian structure of the fin afforded by the presence 

 of a series of soft bifurcate rays in the posterior fold of the natatory integument. 



* Evidences of the structure of the integument of the Ichthyosaurus have not escaped the observation 

 of Dr. Buckland, who has particularly described it in a portion which corresponded with the interspaces 

 of the sterno-costal bones, preserved, as in the present instance, in a specimen from the lias of Barrow- 

 on-Soar. As might have been expected, the scutiform structure is not exhibited in the integuments 

 covering the under surface of the body, but the epidermis here exhibits a fine wrinkled structure. — 

 See Bridgewater Treatise, vol. ii. p. 22. . 



VOL. VI. — SECOND SERIES. 2 D 



