DINOSAURIA. 



211 



support of the dermal armour. All the cervical vertebrae bear short ribs ; 

 the dorsals exhibit especially elevated neural arches on which the stout 

 ril are borne. The sacrum comprises four co-ossified vertebrae, some- 

 times with one or more lumbars added in front; the anterior caudal 

 vertebrae are the largest in the whole series, and the limbs of the 

 chevron bones are not united by a bridge. The fore limb is very power- 

 ful, though small, its most striking feature being the large olecranon 

 process of the ulna. There are only three bones in the proximal carpal 

 series, while the distal carpals seem to have been unossified; and there 

 is imperfect evidence of five digits. The pelvis is extremely massive for 

 the support both of armour and the large hind limbs. The ilium ex- 

 tends far in advance of the acetabulum, and its superior crest curves 



Fro. 130. 



Stegosaurus ungulatua; restoration of skeleton by 0. C. Marsh, one-sixtieth 

 nat. size. Jurassic ; Wyoming. 



inwards to the neural arches of the sacrum with which it is fused. The 

 femur is large and straight, without any inner trochanter, while the tibia 

 and fibula are comparatively short. The astragalus is firmly fused with 

 the tibia, and the calcaneum less securely so with the fibula, while three 

 well-ossified distal tarsals are distinct. The hind foot is imperfectly 

 known, but there seem to be only three functional digits, no. I being 

 rudimentary and no. v entirely wanting. The arrangement of the dermal 

 armour is a little uncertain; but there seems to have been a median 

 crest of very large triangular bony plates along the back, and there are 

 indications of a shield of small rounded ossicles below the mandible 

 and on the throat. Stegosaurug is known only from the Upper Jurassic 



142 



