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 Bidunculus as compared with Goura, in which latter 

 Dove there are articular surfaces for three sternal ribs (PI. XXIV. fig. 3, c i, 2, 3), whilst 

 in Didunculus there are four (ib. fig. 1, c). Diduncidus 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 

 j), fig. 4, PI. XYI., 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 Bidun- 

 culus (PI. XXIV. fig. 1). 



In the direction of the ectolateral processes Goura (ib. fig. 3, h) is intermediate be- 

 tween Bidunculus and Bidus. 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 Bidus. In Goura the subcostal ridge 

 is better marked than in Bidunculus. In no Dove of flight is the body of the sternum 

 so broad and hollow as in Bidus (PI. 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, 

 extendmg 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- 

 dar/jus humeralis). The ectolateral processes (PI. XXIV. fig. 4, /*) 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 Bidus. Moreover the cora- 

 coid grooves are divided from each other by a free concave border, less deep and exten- 

 sive, indeed, than in Bidus, 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 bu-ds, there is an interval 

 between their sternal articulations: this is long and concave in the Dodo, but is 

 longest and most deeply concave in Apteryx; it is long but almost straight in Rhea; in 

 Casuarius and Bromaius it is narrow but deeply notched ; in StrutJiio 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 Bidus and the 

 Rasores, immediately behind the costal margin, but they are continued, parallel with 



