EXTINCT ORDERS OF REPTILES. 477 



the Lower Lias to the Middle Chalk inclusive, the Lithographic 

 Slate of Solenhofen (Upper Oolite) being particularly rich in 

 their remains. Most of them appear to have attained no very 

 great size, but the remains of a species from the Cretaceous 

 rocks have been considered to indicate an animal with more 

 than twenty feet expanse of wing, counting from tip to tip. 



In the genus Pterodactylus proper, the jaws are provided 

 with teeth to their extremities, all the teeth being long and 

 slender. 



In Dimorphodon, the anterior teeth are large and pointed, 

 the posterior teeth small and lancet-shaped. 



In Ramphorhynchus, the anterior' portion of both jaws is 

 edentulous, and may have formed a horny beak, but teeth 

 are present in the hinder portion of the jaws. 



ORDER IX. DINOSAURIA. The' last order of extinct Reptiles 

 is that of the Dinosauria, comprising a group of very remarkable 

 Reptiles, which are in some respects intermediate in their 

 characters between the Struthious Birds and the typical Rep- 

 tiles ; whilst they have been supposed to have affinities to the 

 Pachydermatous Mammals. Most of the Dinosauria were of 

 gigantic size, and the order is defined by the following 

 characters : 



The skin was sometimes naked, sometimes furnished with a 

 well-developed exoskeleton, consisting of bony shields, much 

 resembling those of the Crocodiles. A few of the anterior ver- 

 tebrae were opisthocoelous, the remainder having flat or slightly 

 biconcave bodies. The anterior trunk-ribs were double-headed. 

 The teeth were confined to the jaws and implanted in distinct 

 sockets. There were always two pairs of limbs, and these were 

 strong, furnished with claws, and adapted for terrestrial pro- 

 gression. In some cases the fore-limbs were very small in 

 proportion to the size of the hind-limbs. No clavicles have 

 been discovered. 



The teeth are sometimes implanted in distinct sockets, and 

 they are never anchylosed with the jaws. The ischium and 

 pubes are much elongated ; the inner wall of the acetabulum 

 is formed by membrane ; the tibia has its proximal end pro- 

 longed anteriorly into a strong crest ; and the astragalus is 

 bird-like (Huxley). 



The most remarkable points in the organisation of the 

 Dinosauria are connected with the structure of the pelvis and 

 hind-limb, the characters of which, as pointed out by Huxley, 

 approximate to those of the same parts in the Birds, and 

 especially in the Struthious Birds. This approximation is 

 especially seen in the prolongation of the ilium in front of the 



