STUDIES OF THE MACEOCHIRES. 



371 



different is it ! Quite as different, we may say in trntb, as are 

 the humeri of these birds. 



The tensor patagii longtis in CJiceUira pelagica has the usual 

 origin and insertion that it has in so many of the Class. 



Cypseli and Trochili both possess all three 'pectoral muscles, 

 but in such a form as Micropus they are none of them unduly 

 developed ; better so in Chcetura ; while in the Trochili they are, 

 comparatively speaking, enormously developed. 



Owing to the entirely different shape of the humerus in Swifts 

 and Humming-birds, the tendons of the pectorals make 

 dissimilar insertions. For instance, the pectoralis major in 

 Micropus is inserted upon the entire palmar aspect of the large 

 hook-like radial crest of the humerus of that Swift ; but Trocliilus 

 possessing no such process upon its humerus, the muscle is 

 obliged to insert itself more or less upon the body of the bone, 

 at a point which would be considered as the base, upon the 

 palmar side of a radial process did such a thing exist there. 



Now the 'pectoralis secundiis in Micropus is inserted at the 

 head of the humerus upon its anconal side, between the summit 

 and radial crest or hook ; while in the Humming-bird this second 

 pectoral sends its tendon across the head of the bone, to be 

 inserted at the distal margin of the pneumatic fossa. The 

 insertion of the tliird pectoral in these two groups of birds is 

 more similar. 



So here, again, we see that Swifts and Humming-birds are 

 markedly different with respect to another class of muscles w^hich 

 make up, in part, the fundamental organization of their wing- 

 structures. 



Among the essential characters of the wing we still have left 

 the skeleton, but I have already published my views and drawings 

 in regard to that part of their economy elsewhere (Proc. Zool. 

 Soc. 1885 and 1887). I have there shown conclusively that 

 the humeri of Swifts and Humming-birds are very differently 

 formed bones indeed, and the reader has but to refer to the 

 figures in the papers to which I allude to be convinced upon 

 this point. 



As. I have elsewhere stated, the humerus in Micropus is a 

 non-pneumatic bone as in the Swallows ; while all Humming-birds, 

 so far as I have examined, have pneumatic humeri. Still 

 my statement Proc. (Zool. Soc. 1887, p. 503) requires some 

 modification, for since that was written I have found that the 



