158 STRUCTURE AND CLASSIFICATION OF BIRDS 



relation to nocturnal habits and the presence of a keel upon 

 the sternum. 



It is possible, though far from certain, that Scaphogna- 

 thus had not that characteristic reptilian bone, the os tnnis- 

 versum. 



Finally, the general shape of the scapula and the angle 

 that it makes with the coracoid are birdlike in the pterodac- 

 tyles. 



The brain of the pterodactyles seems also to have pre- 

 sented avian characters ; the optic lobes are pushed aside by 

 the large cerebellum, which had well-developed floccular 

 lobes. In the reptile's brain the optic lobes intervene 

 between the cerebrum and cerebellum. 



The pelvis of the pterodactyles has some likenesses to 

 that of birds. The ilium has an extension in front of as w r ell 

 as behind the acetabulum ; and, if the opinions of SEELEY 

 are to be agreed to, there is a rather backwardly directed 

 pubis, more or less fused with the ischium, and a long and 

 thin forwardly directed piece, the prepubis of dinosaurs and 

 the pectineal process of birds. 



The main difficulty, however, in the w r ay of comparing 

 pterodactyles and birds is in the fact that both can fly, and 

 that each has acquired the power of flight by a different 

 method. Having acquired the power of flight it seems clear 

 that certain of the points of resemblance between them may 

 easily be due to that mode of life and may have been inde- 

 pendently arrived at. 



