DINOSAURIA. 201 



vertebrae are opisthocoelous and much hollowed on each side, 

 with very light neural arch ; the cervical ribs, at least in part, 

 are fused with their respective vertebrae. The neural canal is 

 much expanded in the sacrum, and each sacral vertebra sup- 

 ports its own rib. The pubes project simply downwards and 

 are united distally by cartilage. The limb-bones are solid. 



Some of the Jurassic Sauropoda are the largest known 

 land-animals, the femur of Atlantosaurus immanis from the 

 Upper Jurassic of Colorado, measuring nearly two metres in 

 length. Cetiosaurus oxoniensis, from the Lower Jurassic of 

 England, is smaller. So also is Ornithopsis hulkei from the 

 Wealden of the, Isle of Wight. All these are known only by 

 fragmentary remains, and very similar bones occur in the 

 Jurassic and Cretaceous of Madagascar, of India, and in the 



FIG. 121. 



Brontosaunis excelsus ; restoration of skeleton by 0. C. Marsh, one-one-hundred- 

 and-eightieth nat. size. Jurassic; Wyoming. 



supposed Cretaceous of the Territory of Neuqueu, north of 

 Patagonia. One of the best-preserved skeletons is that of 



Brontosaurus (figs. 121, 122). The head in this reptile is remarkably 

 small, probably smaller in proportion to the body than in any other known 

 reptile. The neck is long and flexible, the body short, the tail much 

 elongated. There are about thirteen cervical vertebrae, with very small 

 neural canal and no neural spines. The hatchet-shaped ribs are fused 

 with the anterior cervicals, but free on those behind ; all the centra 

 exhibit a deep excavation of the sides. The centra of the dorsal vertebrae 

 are short, and their lateral excavations are so deep that they are separated 

 only by a thin median partition. They are opisthocoalous, but a few 

 " lumbars " in advance of the sacrum have flat or slightly excavated ends. 

 The latter vertebrae also bear free ribs of moderate size. The sacrum 

 comprises five vertebrae, and the last " lumbar " is sometimes fused with 



