476 STEUCTUIIE AND CLASSIFICATION OF BI1{J)S 



Milvago cliimanr/o and M. cliima-cliima the syrinx is at first 

 sight perfectly similar, but the intrinsic muscles only just 

 get beyond the first bronchial semi-ring. In Hcrjjctotheres 

 cachinnans this divergence from the normal falconine 

 syrinx is carried still further, the intrinsic muscle being 

 attached to the first semi-ring. 



The syrinx of Polybonis brasiliensis is an exaggeration of 

 the falconine type. The first and second bronchial semi-rings 

 are very prominent and wide apart, thus leaving a very 

 spacious interannular membrane, to which the intrinsic 

 muscles are attached. The last few tracheal rings are fused 

 mesially in front and behind. The remaining forms, so far 

 as I have studied them (comprising the genera Melierax, 

 Nisaetus, Gypaetus, Thrasaetus, Buteo, Milvus, Spizaetux, 

 Urubitinga, Haliaetus, Vnltur, Spilornis, Morphnus, Helo- 

 tarsus, Leucopternis, Circus, Aquila, Circaetus, Gyps, Archi- 

 buteo, Geranoaetus, and Asturina), differ from each other 

 in details such as the completeness or incompleteness of 

 the bronchidesmus, the degree of ossification of the rings 

 and semi-rings, the number of the last tracheal rings which 

 are fused, and the attachment of the intrinsic muscles 

 (semi-rings 1, 2, or 3) but they agree to differ from the 

 falcons in the absence of a pronounced oval gap between 

 the first and second bronchial semi-rings, which gives to 

 the syrinx of the falcons so characteristic an appearance. 



The lobes of the liver are subequal, and a gall bladder 

 is present. The cseca of the Falconidse are minute. 



Haliaetus albicilla is a fish-eating bird, and for some 

 reason birds with such habits are furnished with a long in- 

 testine, as will be seen from the measurements in the table 

 on p. 477. The duodenal loop in this bird, exceptionally, 

 is thrown into a series of subsidiary loops, a state of affairs 

 which, as it occurs in the remote penguin, may have some 

 relation to habits and may not be a character upon which 

 stress is to be laid. The greater part of the intestine pre- 

 serves the simple archaic form of a number of irregular 

 coils ; but near to the caeca are two spirally twisted, elongated 

 loops. In other Accipitres it is more usual for the upper 



