430 



Vertebrata. 



■able, some of colossal size, bigger than tbe largest extant teiTestrial Mammals 

 (in one species the tlugh-bone is 2 — 3 m. long, and very thick) ; though small 

 forms also occur. The limbs are powerful ; in some, fore and hind legs are about 

 equal in length, but generally the former are smaller, sometimes even much 

 feebler than the hind limbs, and many Dinosaurians moved almost entirely upon 

 the latter, possibly springing along ; among those with stronger hind limbs some 

 were digitigrade, whilst other Reptiles are plantigrade; the tail is long 

 and powerful. The pelvis is very remarkable ; the iUa are much prolonged 

 in front of the acetabulum, agreeing with Birds not with Reptiles, and in those 

 Dinosaurians which have small fore limbs (e.g., Iguanodon, Fig. 355), the pubis 

 also is very peculiar in foi-m : a long thin process (p') arises from its base, and 



Fig. 356. A — B fore and hind limts of one of the Dinosaurians, which are some 

 way from birds {Morosaurus grandis). C — D Do. of a bird-Kke Dinosaur (Gamptonotus 

 dispar). a tarsus, c coraooid, d toes, d' fingers, / femur, g fibula, h humerus, i ilium, 

 Ic ischium, m metatarsus, «i' metacarpus, r radius, s scapula, sk pubis, t tibia, u ulna. — 

 After Marsh. 



reaches back, in a dii-ection almost exactly opposite to that of the main branch, 

 l3dng close against, and parallel to the ischium, which is often long and thin. 

 There is a larger number of sacral vertebrae than in other Reptiles (four or more) 

 and these are fused. Among other chai-aoters, it may be mentioned, that the 

 proximal series of tarsals is in many cases immovably attached to the tibia (or 

 fused with it) ; the tibia has a long projecting ridge on its front face. The 

 foi-ms of the femur and tibia are very different from those of other Reptiles 

 and very birdlike. (See also the remarks made below upon avian skeletons.) 

 The Dinosaurians lived in Triassic, Jui-assic, and Cretaceous times. 



Class 5. Aves (Mrds). 



The most striking peculiarity of the avian body lies in the 

 structure of the limbs, the hind are exclusively developed for 

 walking, or hopping (sometimes, also, for swimming), whilst the fore 



