THE WING OF ARCHMOPTERYX. 



355 



Fig. I. 



Fio.II 



P.m. 



PLATE III. 



Fig. I. — The right wing of a nestling Opisthocomus cristatus, ventral view, 

 showing how that the second digit (II.) is produced beyond the ala 

 membrana (P.m.), and that the development of remiges 8-10 has been 

 arrested, so as not to interfere with the freedom of the long finger when 

 climbing. 



Fig. II. — The right wing of a nestling of the Common Fowl (GaUiis hanhiva), 

 an ally of Opisthocomus. Owing to the exchange of an arboreal for a 

 terrestrial habit, the manus is gradually shortening. The poUe.x only 

 retains the claw. The II. digit projects but slightly beyond the ala 

 membrana ; but the development of the most distal remiges is still 

 arrested. 



Fig. III. — The right wing of an adult Opisthocomus cristatus, ventral view. 

 Contrast with that of the young bird, and the manus is now shorter 

 than the forearm, the " poUex " or " thumb " is considerably reduced, 

 as is also digit II. The claw may be seen on the pollex as a slight 

 wart (c). 



i-io. — Metacarpo-digital remiges, or quill feathers. P.m. — Ala mem- 

 brana or posterior wing membrane, c. — Claw. 



2 A 2 



