OSTEOLOGY 145 



processes is most capricious. Thus among the hmicohne 

 series they are absent from the skulls of the gulls and — more 

 unexpectedly perhaps — from the CEdicnemid® and Thino- 

 ooridse. Among the birds of prey the secretary bird and 

 the American vultures have these processes, while the 

 Palconidae have them not. The goatsuckers may be 

 similarly divided into those vyithout and those with basi- 

 pterygoid processes. The Tubinabes, again, show variation 

 in this respect, as do the trogons. It is therefore, in the 

 first place, impossible to compare directly all birds which are 

 vnthout these processes, just as it is impossible to put 

 together all birds without an ambiens. We may note, how- 

 ■ever, that it is only among groups of birds which show a 

 considerable range of structural variation that there is this 

 variation of the basipterygoid processes. It is not, so to 

 speak, lightly that they have gone. The reason for the 

 assumption that the basipterygoid processes are primitive is 

 their existence in reptiles and in such widely separated types 

 as chameleons, pterodactyles, and Hatteria, and in addition 

 I may point out that there is a significant correspondence 

 between a primitive arrangement of gut and the presence 

 of these structures. It cannot be said that every bird with 

 basipterygoid processes has the most primitive arrangement 

 of gut, but we do find both in the ratites, Chauna, the 

 gaUinaceous birds, the charadriiform birds, the owls, and 

 the goatsuckers. The falconiformes (Haliaetus) are, it is 

 true, an exception ; but it must be remembered that this 

 group is one that has basipterygoid processes (Serpentarius, 

 Cathartes), though they are absent in the true falcons. 



The principal variations exhibited by the cranium of 

 birds, apart from those that have been already considered, 

 •concern the existence of supra-orbital bones, the existence oj 

 non-existence of occipital fontanelles, the marks of the supra- 

 orbital glands, and the presence or absence of a hinge line 

 between the skull proper and the face. 



The existence of supra-orbital bones in the form of a 

 longer or shorter chain of ossicles was first pointed out by 

 Parker as a reptilian character of occasional occurrence. 



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