766 The American Naturalist. [September, 
single figure copied by Wiedersheim, has different ideas. He 
has no such projection from the ulnare, but in his figure car- 
pale I+II projects np between radiale and ulnare and the pro- 
jecting portion is the centrale. Zehntner, on the other hand, 
(90) has the intermedium united to the ulnare, the centrale to 
the radiale, conditions which certainly do not occur in Sterna. 
Carpats. Unless we regard the “centrale” of the preced- 
ing paragraph as in reality a carpal, Sterna never possesses 
more than two distinct elements in the distal carpal series. 
Of these that on the radial side is the larger. When chondri- 
fication begins it occupies a position (fig. 2) at the base of met- 
acarpal IIL; later (figs. 3, 4) it extends radially towards meta- 
carpal II, and even at times (fig. 4) exhibits a marked bilobate 
appearance. From these facts as well as its subsequent his- 
tory I regard it as a compound body, the carpales II--III of 
the normal pentadactyle hand, the distal carpal II of Parker 
and most other students of Avian osteology. Concerning the 
.'* pentosteon " of Shufeldt I can say little. This author (’82° 
p. 691, footnote) gives this name to a small bone found by him 
in Centrocercus lying at the base of the plantar surface of the 
second (my third) metacarpal. The name was given because 
it was the fifth carpal bone discovered, and because it was non- 
committal as to its homologies. Parker now finds the same 
bone in ducks and auks, occupying the same position, and re- 
gards it as carpale I. This interpretation, however, seems to 
me faulty, as the bone is not in the proper position for such 
identification, nor have we any torsion or stress which could 
account for such translation. It would appear rather to be- 
long to the same category as the pisiforme, but since I have 
not found it in Sterna I can offer no further observations upon 
it. | 
The other free carpal element, carpale IV, is clearly but a 
single element and not a compound structure like that de- 
scribed by Zehntner, Rosenberg and others. Studer, in the 
penguin, also figures a broad element in this position which 
he doubtfully regards as compound. In Sterna this element 
at its first differentiation is no wider than the fourth metacar- 
pal, and as long as it retains its free condition it remains re- 
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