SKELETON 4 I 5 



for the insertion of the long caudi - femoral or long adductor 

 muscle. 



Many Dinosaurs possess hollow instead of solid bones. The 

 vertebrae have large cavities in the Sauropoda, notably in Uronto- 

 saurus ; in many Theropoda, e.g. Ooelurus, Anchisaurus, Compso- 

 gnathus, the limb-bones and the vertebrae are hollow, the latter 

 being reduced to thin- walled shells with a few inner partitions, the 

 bones being at the same time much swollen and enlarged. In 

 the Ornithopoda the vertebrae are solid, but the limb-bones are 

 hollow. The reason of this hollowing out is not easily found. 

 Undoubtedly it results in a saving of material and weight, 

 whilst at the same time, without loss of strength, the surfaces for 

 the attachment of the necessarily powerful muscles are increased. 

 But Compsognathus is a small, Brontozoum a gigantic, creature. 

 On the other hand, the bones of the huge Stegosauri are solid. 

 Most probably these cavities were, as in birds, filled with air-sacs 

 ultimately in communication with the lungs ; and it is by no means 

 a baseless suggestion of Haeckel's that the Dinosaurs were warm- 

 blooded. Their mode of propagation can only be guessed at 

 from the circumstance that a rather well-preserved specimen of 

 Compsognathus contains in its abdomen what may possibly be 

 an embryo. There is nothing against the assumption that the 

 Dinosaurs were viviparous ; on the contrary, it seems more 

 natural than that, for instance, an Atlantosaurus of more than 

 100 feet in length and many tons in weight, should have laid 

 eggs. 



Some of the herbivorous Dinosaurs, namely, the Stegosauri 

 and the Ceratopsia, had a dermal armour of variable extent ; the 

 plates were loosely imbedded in the skin, and reached their 

 greatest size along the middle of the back and tail, and these 

 crested plates were probably covered with horny scutes, 

 obviously weapons of defence. The Ceratopsia were armed with 

 a pair of huge pointed horns on the head, and a smaller one on 

 the nose (see Fig. 102, p. 430). It is difficult to guess the 

 use of the weapons of these, terrestrial monsters, unless they were 

 employed against the equally large carnivorous Dinosaurs or in 

 the combats for the possession of their charming mates. 



About the ancestry of the Dinosaurs we know nothing except 

 that their affinities lie with the Crocodilia ; but it is impossible 

 to derive either from the other. The oldest forms, in the 



