242 STRUCTURE AND CLASSIFICATION OF BIRDS 



in Podargus. The spina externa is developed and slightly 

 bifurcate in Steatornis. There is no spina interna. 



In view of the considerable variation in structure ex- 

 hibited by the group, the follovying tabular statement may 

 be of use. 



There can be little doubt, from a consideration of the 

 above table, of the naturalness of a family Caprimulgidae to 

 include the last four genenu. In these forms, in all of them, 

 the toes are aberrant in that the last has only four phalanges, 

 and further that the claw of the middle one is serrated. 



It will be noticed from the table that the amount of 

 structural variation among the Caprimulgidae (s.s.) is exceed- 

 ingly small, the only character, indeed, of those selected 

 which varies being the gall bladder, which is absent in 

 Chordeiles, and shows signs of commencing disappearance 

 by its small size in some of the others. We might, perhaps, 

 add the desmognathism of Chordeiles ; but this is obviously 

 but a slight exaggeration of the segithognathous palate of 

 the others. The enormous length of the second primary of 

 Macrodipteryx a.T\d Cosmetornis is a variation which does not 

 appear to be of great importance from a classificatory point 

 of view. 



The remaining genera are by no means so uniform a 

 group as that which those that have been already considered 

 form. In all of them, however (so far as is known), the 

 biceps slip is absent, the glutaeus primus is of limited extent, 



■ See Blyth in Ibis, 1866, p. 357. 



