376 REPTILIA. 



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. DEINOSAURIA. The last order of the Reptiles 

 is that of the Deinosauria, comprising a group of very remark- 

 able extinct forms, which are in some respects intermediate in 

 their characters between the Cursorial birds and the typical 

 Reptiles ; whilst they have been supposed to have affinities 

 to the Pachydermatous Mammals. Most of the Dtinosauria 

 were of gigantic size, and the order is denned 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 

 progression. 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 

 Deinosauria 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 

 acetabulum (fig. 325), the elongation and slenderness of form 

 of the ischium, and the slenderness of the pubes. The astra- 

 galus is like that of a bird, and in some cases appears to have 

 become anchylosed with the distal end of the tibia. The 

 metatarsal bones, however, remain distinct, and are not an- 

 chylosed with any of the tarsal bones to form a " tarso-meta- 

 tarsus." 



