372 
1)R. R. W. SHUFELDt’s MORPHOLOGICAL 
humeri in Chcetura pelagica are pneumatic, but the bone is 
shaped upon the same plan as the humerus of Micropus, and the 
pneumatic fossa is, as in Passeres, on the ulnar side. Prom 
what has gone before, we now know that in general form, and 
other particulars, Micropus is nearer the Swallows than is such 
a Swift as Chcetura, and this last fact, with respect to the arm- 
bones, points still more strongly to the truth of such a state- 
ment. Even at this moment I am not acquainted with any other 
bird in the Class that has the pneumatic fossa of its humerus 
situated on the radial side of the bone, as the Trochili have. 
This fact alone, and surely when taken in connection with the 
otherwise vastly different form of the bone itself, is sufficient to 
show that in their wing-structure Swifts and Humming-birds 
widely differ. 
Purther, in the papers above alluded to I have already 
pointed out how' in the bones of the antibrachium, in Tro- 
chilus and Micropus, the radius is actually bent to a bow in the 
former, while it is as absolutely straight as any bone can be in 
the Swift. The ulna, too, in these birds differs in its general 
form. Moreover, w-e find sesamoids present in the carpus of 
Humming-birds which do not exist in Cypseli, although, since 
writing my first memoir on this subject, I have found a sesamoid 
at the elbow in Chcetura and Micropus, such as the Sw'allows have. 
Coming next to the carpo-metacarpus we find one great 
and principal difference, in addition to minor ones — in the Hum- 
ming-birds the middle metacarpal in this compound bone is 
longer than the index metacarpal, the reverse condition obtain- 
ing among the Swifts. This is enough to show that the bones 
are essentially unlike in their most important character. The 
proximal phalanx of the index finger is altogether a differently 
formed bone from the corresponding segment in the mauus 
of the Swift, as any one may see by a comparison either of the 
bones themselves or my drawings (P. Z. S. 1S85, pi. Ixi. figs. 3 
and 4 ,j). 
To briefly recapitulate, then, the absolutely essential and 
fundamental characters in the wing-structure of a Swift and a 
Humming-bird, I find that : — 1. The parts markedly differ in 
their external characters, inasmuch as they do not possess the 
same number of secondary quill-feathers ; Swdfts have a very 
peculiar pigmented (deep black) area of the skin centrally located 
on both sides of the hand, while Trochili have not; the character 
