43 
margins behind the ectolateral processes (ib. fig. 1, A), instead of converging with a 
slight convexity to an obtuse apex, as in PI. VI., describe a concavity, through an 
expansion of the posterior truncate end of the breast-bone. The sternum of Didunculus 
may be said to show one pair of posterior notches (PI. XII. fig. I,/), that of other 
Pigeons two pairs (ib. fig. 3, ff) ; but the sternum of Didus, which is relatively broader, 
shows no other trace of the anterior notch (PI. VI. f) than is afibrded by the 
rounded angle at which the ectolateral process (A) rises from the bone. Although the 
costal margin is relatively shorter in Doves of flight than in the Dodo, again an inter- 
mediate condition is manifested by Didunmlm as compared with Goura^ in which latter 
Dove there are articular surfaces for three sternal ribs (PL XII. fig. 3, c i, 2 . s), whilst 
in Didunculus there are four (ib. fig. 1, c). Didunculus also exhibits, more strongly 
than Goura, the obtuse ridges (ib. fig. 2, r) converging like buttresses from the outer 
wall of the coracoid groove to the fore part of the keel, where they subside. In Didun- 
culus there is a pneumatic foramen exterior to the coracoid groove, corresponding with 
p, fig. 4, PI. IV., which I do not find in the sternum of Goura; but in the Crown- 
pigeons the pneumatic foramina along the middle line of the upper surface of the 
sternum are conspicuous ; they are confined to the fore part of that surface in Didun- 
culus (PI. XII. fig. I). 
In the direction of the ectolateral processes Goura (ib. fig. 3, A) is intermediate be- 
tween Didunculus and Didus. The pectoral ridge on the outer surface of the sternum, 
continued backward from the outer end of the coracoid groove, is adaptively better marked 
in Pigeons of fiight than in the Dodo ; and the pair of ridges are more nearly parallel 
in their backward course, not so convergent as in Didus. In Goura the subcostal ridge 
is better marked than in Didunculus. In no Dove of fiight is the body of the sternum 
so broad and hollow as in Didus (PI. XI. fig. 4) ; in this respect the Vulture more 
nearly resembles the Dodo, as it does also in the more convex anterior contour of the 
keel ; but the vulturine sternum does not lose breadth as it extends backward ; it is a 
square-shaped shield in birds of prey, shorter in proportion to its breadth, with a greater 
extent of costal process and margin, and with the ectolateral processes, when they exist, 
extending backward as far as the hinder border of the bone. In the thorough quest of 
resemblances to the Dodo’s sternum which I have made through the class of Birds, I 
came upon an unexpected superficial likeness to it in the sternum of a Night-jar 
{Podargus humeralis). The ectolateral processes (PI. XII. fig. 4, A) rise behind the 
moderately extended costal borders, c ; and beyond them the body of the sternum con- 
verges to an obtuse end, with a contour similar to that in Didus. Moreover the cora- 
coid grooves are divided from each other by a free concave border, less deep and exten- 
sive, indeed, than in Didus, but as free from any trace of episternal projection. The 
ectolateral processes, however, are extended backward to beyond the sternal body ; and 
this part usually shows a pair of small entolateral notches, f, of which one was present 
on one side in the specimen figured. 
G 2 
