ICTHYOSAURUS. 567 



But the progression of these animals through the water was 

 accomplished in part by means of the anterior and posterior 



F/o. 337 ICTHYOSAURUS. 



extremities, which are very efficient instruments of propulsion, 

 being formed very much upon the plan of the paddles of the 

 Whale ; but their number of fingers and phalanges was 

 much greater; and the bones themselves, being shorter, were 

 arranged in a tessellated manner. The muzzle is elongated and 

 pointed ; and the teeth very numerous. The general form of 

 the head is not unlike that of the Porpoise ; but it must have 

 had far greater strength, and the surface for the attachment of 

 muscles is very extensive. The form and solidity of the sternal 

 arch, to which the anterior paddles are attached, show that 

 provision was made for imparting enormous power and firm- 

 ness to these ; and certain peculiarities in the structure of the 

 tail seem to prove, that the Icthyosaurus must have had a ver- 

 tical cartilaginous tail-fin, like that which is seen on the back of 

 many Cetacea. From the absence of any remains of scales or 

 plates, it may be concluded that the skin was naked, like that 

 of the Whales and their allies. There is no question that the 

 Icthyosaurus was exclusively an air-breathing animal ; no trace 

 of any adaptation to branchial respiration being perceptible. 

 From the remains of partially-digested food, which are found 

 with their bones, it appears that they fed (as might have been 

 anticipated) exclusively upon Fishes ; and especially upon one 

 species, which is known only in a fossil state. Some of the 

 largest of these aquatic Reptiles must have exceeded thirty feet 

 in length; and it is easily to be conceived that 'they were very 

 formidable enemies to the other inhabitants of the deep. They 

 seem to have taken the place of the Grampus, and other vora- 

 cious Cetacea, at a time when no Mammals had been called into 

 existence. 



