230 



EXTINCT OP.DERS OF REPTILES. 



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

 The teeth were confined to the jaws and implanted in distinct 

 socJcets. There ivcre always two pairs of limbs, and these were 

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

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

 jjortion 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 

 piibes are much elongated ; the inner wall of the acetabulum 

 is formed by membrane ; the tibia has its proximal end 



prolonged anteriorly into a 

 strong " cnemial crest," as in 

 the wading or swimming 

 birds ; and the astragalus is 

 bird-like (Huxley). 



The most remarkable points 

 in the organisation of the 

 Deinosauria are connected 

 with the structure of the pel- 

 vis and hind-limb, the charac- 

 ters of which, as pointed out 

 by Huxley, approximate to 

 those of the same parts in the 

 Birds, and especially in the 

 Struthious Birds. This ap- 

 proximation is especially seen 

 in the prolongation of the 

 ilium in front of the acetabu- 

 lum (fig. 576), the elongation 

 and slenderness of form of 

 the ischium, and the slender- 

 ness of the pubes. The as- 

 tragalus is like that of a bird, 

 and in some cases appears to 

 have become anchylosed with the distal end of the tibia. 

 Generally, however, the astragalus remains distinct, but even 

 in this case the ankle-joint is placed between the astragalus 

 and the distal portion of the tarsus. The metatarsal bones 



Fig. 57G. — Leg of Deinosaur. il, Ilium ; 



is, Ischium ; /, Femur ; i. Tibia ; s, Fibula ; 



as, Astragalus ; ca, Calcaneum ; m, Meta- 

 tarsus. (After Huxley.) 



