74 PROFESSOR OWEN ON THE 
costal margin is relatively shorter in Doves of flight than in the Dodo, again an inter- 
mediate condition is manifested by Didunculus as compared with Goura, in which latter 
Dove there are articular surfaces for three sternal ribs (Pl. XXIV. fig. 3, ¢ 1, 2,3), whilst 
in Didunculus there are four (ib. fig. 1, ¢). Diduneulus also exhibits, more strongly 
than Goura, the obtuse ridges (ib. fig. 2,7) 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, Pl. XVI., 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 (Pl. XXIV. fig. 1). 
In the direction of the ectolateral processes Goura (ib. fig. 3, 2) 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 flight than in the Dodo; and the pair of ridges are more nearly parallel 
in their backward course, not so convergent as in Didus. In Gowra the subcostal ridge 
is better marked than in Didunculus. In no Dove of flight is the body of the sternum 
so broad and hollow as in Didus (Pl. XXIII. 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 (Po- 
dargus humeralis), The ectolateral processes (Pl. XXIV. fig. 4, h) rise behind the 
moderately extended costal borders, ¢; 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, /’, of which one was present 
on one side in the specimen figured, 
Through the reduction of the coracoids in all flightless birds, there is an interval 
between their sternal articulations: this is long and concaye in the Dodo, but is 
longest and most deeply concave in Apterya; it is long but almost straight in Rhea; in 
Casuarius and Dromaius it is narrow but deeply notched ; in St¢ruthio it developes a short 
episternal process, In no Grallatorial sternum with both ecto- and ento-lateral pro- 
cesses (as e.g. Otis, Edicnemus, Charadrius) do the former project, as in Didus and the 
Rasores, immediately behind the costal margin, but they are continued, parallel with 
