122 STEUCTURE AND CLASSIFICATION OF BIRDS 



muscles, has been clearly pointed out by T. J. Parker.' He 

 discovered an approximation to the struthious condition in 

 several of the flightless rails and other birds. But the state 

 of affairs which characterises the Tubinares warns us against 

 placing too much rehance upon this apparently sound gene- 

 rahsation ; for in them we are informed by Forbes that 

 ' the angle it ' (the scapula) ' forms with the coracoid varies 

 much in different genera, being most acute in Pelecanoides, 

 whilst in the Oceanitidse it is hardly if at all less than a right 



Fig. 69. — Development of Shouldek Gibdle op Chick (afteb Lindsay). 



d, clavicle ; pe^ procoracold ; cor, coracoid ; sc, scapula, 1-3, fifth day ; 4, sixth day ; 

 5, late on sixth day. 



angle.' The widest angle in a carinate bird is 106°, so there 

 is a difference of only 16° between extremes of carinates and 

 ratites. 



The two clavicles ^ sometimes spoken of collectively as 

 the furcula vary much in their degree of development. They 

 are totally absent in the Apteryx. In the emu and in certain 

 parrots they are distinct and smallish bones which do not 

 come into contact with each other ; but in the majority of 

 birds they form a single U- or V-shaped bone. 



The furcula varies in the expansion or non-expansion of 

 the base to form a circular hypocleidium. In some birds the 



' ' On Notornis,' in Tr. N. Zealand Inst. xiv. 1882. 



^ A. Weitzel, ' Die Furcula : ein Beitrag zur Osteologie der Vogel,' Zeitschr. 

 f. d. ges. Naturw. xxv. 1865, p. 317. 



