1894.] Development of the Wing of Sterna wilsonii. 763 
III and IV have become longer, III and IV being segmented. 
The fourth digit has become free from the central mass, and 
more nearly approximated to digit IV. In the distal carpal 
series there are two masses of cartilage: on the radial side a 
mass which represents the combined carpales II and III, and 
on the side of the ulna carpale IV, an oval mass contiguous 
proximally to the distal lobe of the ulnare and distally to its 
own metacarpal. 
Srace III, (Fro. 3). 
In this stage (fig. c) there are several things to be noted. 
The spreading of the digits is not so great and the whole 
manus is beginning to flex towards the ulnar side, thereby dis- 
placing some of the carpals from their normal position. The 
elements are now all perfectly distinct, the radiale has entirely 
lost its bibobate appearance, and is now of an irregular shape, 
touching the radius and ulna and the approximate surface of 
the conjoined carpales II and III. The ulnare is now entirely 
outside the ulna, but, what seems most remarkable, its proxi- 
mal portion is now about twice the size of its distal lobe, 
while in the stages previously described it is about half as 
large. The distal lobe is circular, the proximal wedge-shaped, 
with the small end proximal. Carpale II--III is the last car- 
pale to chondrify, but is now all cartilage except a very small 
portion of its proximal end. It isan elongate mass, placed 
somewhat diagonally to the present axis of the limb. It is 
contiguous distally to the approximate surface of metacarpals 
II and III and carpale IV ; proximally to the radiale. Carpale 
IV retains the same relative position as in earlier, except that 
it has approached closer to metacarpal III. Digits II and IIT 
have each added a segment, that of the former is partly car- 
tilaginous, the latter is all procartilage. Metacarpal IV has 
approached metacarpal III and its single phalanx is entirely 
cartilaginous. Metacarpal V has the same appearance as in 
previous stages, but is farther from metacarpal IV. 
Srace IV, (Fie. 4). 
The specimen which forms the subject of this stage (fig. d) 
is in some respects slightly more developed than stage III, in 
