166 STBUCTUJRE AND CLASSIFICATION OF BIRDS 



of a penguin, where the bones show greater traces than 

 in any other birds of their distinctness, and are furthermore 

 shorter than is the rule. In dinosaurs generally those bones 

 are separate, but not in Ceratosaurus, where the degree of 

 fusion is almost exactly that of Aptenodytes. 



Furthermore in some dinosaurs, as in birds, the inter- 

 medium is prolonged upwards as the ascending process of 

 the astragalus. 



The proportions of the long bones of the hind limb are 

 distinctly birdlike in some dinosaurs. In Laosaurus, for 

 example, the femur, as in birds, is shorter than the tibia, the 

 reverse occurring in most forms. In the same animal and 

 in others the fibula is commencing to degenerate ; it is 

 decidedly smaller than the tibia. 



In their skulls the dinosaurs show no marked approxima- 

 tion to birds ; there are nevertheless one or two features 

 which may be remarked upon in this connection. The 

 earliest known forms from the Trias have perhaps the most ' 

 birdlike forms of skull. Marsh comments upon the light- 

 ness and avian appearance of the skull of Anchisaurus ; it 

 has moderately developed basipterygoid processes instead of 

 those of such great length that are apt to characterise the 

 dinosaurs. The great extension backwards of the premaxil- 

 laries in some dinosaurs is an avian characteristic ; this is 

 seen especially well in Diplodocus and Claosaurus. In the 

 former animal, as in some others, the two vomers diverge 

 widely posteriorly, as in many birds ; and in the restoration 

 of the under surface of the skull in this dinosaur the vomers 

 have a very birdlike appearance. 



Finally the height at which the transverse processes of 

 the vertebrae are borne seems, as Huxley has pointed out, 

 to suggest birdlike respiratory organs, while the hollowness 

 of many of the bones in many dinosaurs points in the same 

 direction. It is, however, undoubtedly in the pelvis and 

 hind limb that the most striking likenesses to birds are 

 shown by the dinosaurs. It has been attempted to put this 

 down merely to bipedal progression. 'It may be said,' 

 remarked Professor Hxjxley, ' that all birds stand upon 



