70 PROP. W. K. PAEKEE ON THE 



radiale ; it lies on the outer or extensor side of the wrist. On the uhiar side of 

 the wrist, instead of the thick, two-lobed U-shaped carpal so familiar to us in all adult 

 birds, there is, on the flexor side, a pear-shaped carpal {ue.\ the ulnare proper, which 

 sends its narrow end forwards to articulate with the third metacarpal and its distal 

 carpal [mo?, d.c.^), and which overlaps at its broad end the bulbous distal end of the 

 ulna (?«.). The shorter thicker crus of the bilobate ulnare of the adult is here repre- 

 sented by a subcrescentic mass which, behind, is attached to the ulna and free ulnare, 

 and in front by ligament to the second and third distal carpals {d.c.-, d.c?) at their 

 junction, and also to the postero-distal angle of the intermedium (?'.). A transverse 

 chink on the inner face of the mass partially subdivides this centrale into an anterior 

 and a posterior segment (c, c.^). These are all the proximal carpals I find in this 

 bird ; the distal carpals are three in number, and are constant throughout the 

 Carinatae, corresponding to the three constantly developed digits. The second and 

 third distal carpals {d.c.^, d.c?) are formed from one mass in the early embryo, but the 

 hinder and lesser nucleus is soon detached, and then coalesces again with the larger 

 piece {op. cit. pi. vi. figs. 1-4, d.c.^, d.c.^). The line of segmentation of these two 

 carpals, at a stage a little earlier than this, is indicated by the direction of the cells of 

 the cartilage, which, in the two regions, curve from each other back to back, thus 

 leaving a fine clear tract between the groups of cells. This is soon obliterated, so 

 rapid is the metamorphosis of the parts in these hot-blooded, fast-growing types. The 

 intense growth of the second carpal, metacarpal, and digit, which form the main part 

 of the framework, for the insertion of the primary quills, has dominated the whole 

 manus, and has thrown the elements of the limb out of gear. The third distal carpal 

 lies along the ulnar or hinder side of the second, and is as much lessened as the meta- 

 carpal [mc.^) that belongs to it ; the two together form a remarkable grooved trochlea 

 on which the proximal carpals roll. The latter are more tightly strapped to the 

 radius and ulna, and here, as in the hind limb, the main movement is between the 

 proximal and distal row of segments. Were there fusion of the proximal carpals with 

 the radius, and did the ulna end in a point, dissimilarity would be complete. Of what 

 service the "alula" is to the bird in flight it is diflcicult to say; it cannot be of much, 

 as it gives but a slight increase of size to the wing, and that only near the carpal bend. 

 Certain it is that the larger the manus the lesser is the pollex, as we see in the 

 " Macrochires," the Swifts, and Humming-birds. But here, in this Eeptilian bird, the 

 pollex is relatively nearly as large as in Man (PL X. figs. 1-7) ; that is, it is so in the 

 embryo, not in the adult (figs. 8, 9). The condition of the first distal carpal is very 

 remarkable ; it is a small limpet-shaped cartilage, attached to the head of the first 

 metacarpal on its flexor face (PI. X. figs. 2, 3, 7, d.c}). I can give no other inter- 

 pretation to Dr. E. W. Shufeldt's " pentostium " ^. 



' See liis " Osteology of the Norlh-American Tetraonidte," Geological Survey of the Territories, Washington 

 Oct. 14, 18S2, pi. vii. fig. 59, 8. 



