1903. | OSTEOLOGY OF THE CUCULIFORMES. 275 
and extend more than halfway down the sternal segment of the 
Ath rib as in Seythrops. 
The sternal ribs of Coua reynaudi ave relatively longer than in 
other Cuckoos, and this fact appears to be correlated with 
degenerate powers of flight. As a result of the lengthened rib- 
segments and a change in the angle formed by the corpus sterni 
and the vertebral column, to be discussed presently, the form of 
the thoracic cavity differs conspicuously from that of other Cuckoos 
and recalls features characteristic of ‘“ Ratite.” These peculiar 
features ave wanting in Cowa cerulea. 
The cervical ribs of the Musophagi closely resemble those of 
the Cuculi, taking the form of broad pleurapophyseal lamelle. 
From the 5th to the 8th these lamelle are fenestrated as in the 
Cuckoos, so that the lamella appears to be joined to the centrum 
by a slender bar of bone, the bar extending to the level of the base 
of the postzygapophysis. There are six pairs of thoracic ribs, five 
of which articulate with the sternum. The 6th pair are long, 
but have lost connection with their sternal segments, which 
remain as small spicules anchylosed with the sternal segment of 
the 5th pair. In the Cuckoos, it will be remembered, there 
are only 5 pairs of thoracic ribs, the 5th pair of which, like the 
6th in the Musophagi, fails to reach the sternum. 
vi. THE STERNUM AND SHOULDER-GIRDLE. 
The sternum of the Cuculiformes recalls that of the Coraci 
rather than that of any other group. 
The sternum of the Cuculi may be readily distinguished from 
that of the Musophagi in that it is relatively conspicuously shorter, 
being indeed in many cases as broad as long. Moreover it 
appears to be undergoing yet further reduction. 
The form of the posterior margin of the corpus sterni and the 
relative development of the spina eaterna present considerable 
variations. 
With regard to the posterior margin of the sternum, this appears 
to be entire in Cacomantis only. Two extremely thin oval areas 
indicate, however, the presence originally of a pair of posterior 
lateral processes, the space between which and the median border 
of the metasternum has been filled up. ; 
In Scythrops, Cuculus, Coccystes, Guira, Centropus, and Croto- 
phaga the posterior border is interrupted by a single pair of 
notches, the outside of the notch being bounded by the posterior 
lateral process. 
All the other genera appear to have a doubly notched sternum, 
but the character of the notches varies considerably. In Piaya, 
for example, the posterior lateral process arises directly behind the 
articulation of the 4th rib, and extends outwards and backwards 
to terminate in a spatulate extremity some distance cephalad of a 
line passing across the free border of the metasternum, Between 
this process and the metasternum is a straight processus intermedius, 
