i8S6.] Lucas on the Affinities of ChcEtura. 449 



pression of the shaft, the elongation of the distal head, and the 

 exaggeration of all ridges.* The shortness of the humerus in 

 TrocJiihis is remarkable, but in this particular it is equalled by 

 CJuvtura^ while the strange development of the radial ridge in 

 this latter bird is, so far as I am aware, peculiar to the Swifts. 

 The humerus of Chelidoji is merely that of any typical Passerine 

 a little shortened. Os /i7imero-scap7ilai-c i?, Y'Ye?,e\\t in CheUdon^ 

 but I have been unable to find it either in Chcrtttra or Trochihis. 

 This, however, does not signify much, for this little bone is found 

 in such a distant relative of the Passeres as Steato7'nis. Tro- 

 chihis has two anconeal sesamoids ; Chcetura^ Chelidon^ and 

 many Passerines have but one.f 



The curious, straight antebrachium of Chc^tura is apparently 

 another peculiarity of the Swifts, and bears no resemblance 

 whatever to the forearm of either Trochihis^ C/iclidon, or 

 Chordeiles. The radius and ulna ol Trochihis are strongly 

 bowed outward from one another, an arrangement which prob- 

 ably has some direct relation to the rapidity with which the wing 

 is moved, for the same thing occurs in Tiiiamiis^ and to a less 

 degree in the Gallina:', and these birds are noted for tlieir rapid 

 wing beats. The principal ])one of the carpus, the ulnare, is 

 very similar in both Trochihis and Chcetu radii's, inner side being 

 prolonged into a process which overlaps, or underlies the meta- 

 carpus. The ulnare of Chordeiles resembles that of Chivtiira^ 

 but the ulnare of Chchdon has the roughly trihedral shape cus- 

 tomary among the Passeres. The second metacarpal of Chcetura 

 is round, as in Trochihis and Chordeiles, and is very difterent 

 from the broad, flat metacarpal of ChcUdon, AmpeUs^ and other 

 passerine birds. Its length in comparison with the ulna is the 

 same in Chcvtiira and Trochiliis. 



The first phalanx of the second digit is proportionally much 



* A word in regard to variation. Apparently tlie smaller the bird the more exag- 

 gerated the characters of its bones. Thus little Sclasphoriis with its narrow wings has 

 in proportion to its size a more widely forked furculum, a stouter and more rugose 

 humerus, and deeper sternal keel than its larger relative Campylopterus. 



fThe majority of passerine birds dissected by me have an anconeal sesamoid, one 

 on the ulnar side of the carpus, and one on the anterior edge of the wing at the base 

 of the first phalanx of the second digit. I am inclined to believe that these sesamoids 

 are seldom if ever lacking in Passeres except when lost in preparation, as may readily 

 happen. 



