1885.] TROCHILID.E, CAPRIMULGID^, AND CYPSELIDyE. 909 



with the similar points in the corresponding limb of Pani/ptila saxa- 

 tilis as shown in figure 4, we find that scarcely one of thein exactly 

 agrees with the other. Indeed, the differences are very striking and 

 important, and far greater than commonly occur among birds 

 generally. 



To commence with, the humerus in the Swift, though short, is of 

 entirely a different form. Its radial crest curves towards the humeral 

 head ; the ulnar crest is powerfully developed, though the fossa it 

 arches over contains no pneumatic opening, the bone not enjoying 

 this property as does the humerus in Trochilus. Again, the apo- 

 physis at the base of this fossa is not found in the Swift as it was 

 in the Humming-bird, though in the former a distinctive tubercle 

 occurs beyond the base of the radial crest, which is absent in the 

 latter. 



The olecranon fossa is even deeper and better defined than in 

 Trochilus, though I have failed to find any of the sesamoids present 

 in the limit of that little bird ; and among these the large one which 

 corresponds to the one marked s in figure 3. Pamjptila has the 

 oblique and ulnar tubercles of this distal humeral extremity also 

 markedly protuberant. 



Radius and ulna are here both very straight, and differ from the 

 Humming-bird in being appreciably longer than the bone of the 

 brachium. 



Ul/iare and radiale segments of the carpus deviate but slightly 

 from the general contour of these bonelets in Passeres, and still less 

 from them as found in some Swallows. 



Metacarpus is comparatively large and heavy, its form being well 

 shown in fig. 4. It will likewise be observed that the digital formula 

 agrees with the Trochilidce, as it does with Passerine types ; the 

 individual bones, however, have forms peculiar to themselves. These 

 can be best appreciated by a study of them in the Plate, and far 

 better than can be conveyed in any written description. 



Huxley, in alluding to the relative lengths of the bones of the 

 pectoral limb in the Trochilidce and Cypselidce., says that tlie " two 

 families have a length of the manus and a brevity of the humerus 

 which is peculiar to themselves, being only approached by the 

 Swallows, and in a less degree by the Caprimulgidce. 



" In both Caprimulgus and ^gotheles the manus is slightly 

 longer than the ulna, and the latter considerably exceeds the humerus 

 in length." ' 



My studies of the skeletons of American forms of these several 

 families fully bear out the results of the investigations of this eminent 

 biologist upon this point. 



Owing to the fact that the structure of the foot and certain parts 

 of the pelvic limb can be studied from external inspection with 

 results far more satisfactory than can be hoped for, from the very 

 nature of things, from an equal amount of attention paid to the wing 

 of a bird, it stands to reason that, as a rule, these parts, so far as 



1 " On the Classificatiou of Birds," P. Z. S. 1867, p. 4G9. 

 Proc. Zool. Soc— 1885, No. LIX. 59 



