276 MR. W. P. PYCRAFT ON THE [ Mar. ris 
which, like the external process, fails to reach the level of the meta- 
sternal border. In Rhinococcyx, Rhamphococeyx, and Taccocoua 
the posterior lateral process arises, as in Piaya, immediately behind 
the articulation for the 4th rib, but it forms a wider angle with 
the long axis of the sternum, and carries with it the intermediate 
process, so that it looks like a branch thereof. In Cowa and Geo- 
coccyx the posterior lateral process leaves the sternal plate further 
back than in the forms just described. In other respects these 
two sterna are quite distinct. 
In Coua cerulea the posterior lateral process is very broad, and 
extends backwards to the level of the posterior border of the meta- 
sternum, whilst theintermediate processisshortand normaily placed. 
Coua reynaudi, with an obviously degenerate sternum, differs from 
C. cerulea in that the posterior lateral process is slender, and the 
intermediate process shows a tendency to fuse with the base of 
the posterior lateral. In Geococcyx the posterior lateral process 
is long and slender, but fails to reach the level of the free border 
of the metasternum ; whilst the intermediate process lies nearer the 
posterior lateral than the metasternum. Further, the sternum is 
peculiar in the great depth of the fissure on either side of the 
metasternum, giving this a long and narrow shape. 
A conspicuous pointed spina externa is found in Guira, Cuculus, 
Geococcyx, and Scythrops. It is vestigial in Centropus. A small 
spina interna occurs in Taccocoua. 
In Rhamphococcyx the spina externa and interna are both 
present, and fused to form a moderately large spina communis. In 
Piaya, Rhinococcyx, and Coua there is a vestigial spina communis. 
In Cacomantis the two spines remain distinct, but are extremely 
reduced. A 
Both sping externa and interna are wanting in Crotophaga. 
The carina sternt is relatively largest in Cuculus (text-fig. 43, 
p. 277), Cacomantis, and Scythrops. Its free ventral border is 
strongly arched, and its anterior border is deeply concave. The 
antero-ventral angle of the keel affords a firm articulation for the 
fureula. In Coua, Rhamphococcyx, Crotophaga, and Piaya, the 
anterior border of the keel is very deeply emarginate, causing the 
free border of the kee! to project forward in the form of a long 
style. With the dorsal surface of the style the clavicle articulates 
by means of a long hypocleideum. Apparently the length of the 
hypocleideum is directly correlated with the retreat of the carina 
caudad. In the Galli this is well seen, the climax being attained 
in Opisthocomus. 
The depth of the carina is extremely reduced in Coua reynaude 
(text-fig. 44, p. 277), so much so indeed that the power of flight 
in this species must be extremely limited. In other Cuckoos the 
depth of the carina is nearly or quite equal to half the breadth of 
the corpus sterni; in the species in question the greatest depth 
of the keel is barely one-fourth the breadth of the sternal plate. 
Correlated with the reduction in the keel and the consequent loss 
of flight, is a marked change in the position of the sternum, which 
