The ribs of the Dodo are as broad, in proportion to their length, as in Doves, but are relatively longer in proportion to the dorsal region, encompassing a more capacious thoracic-abdominal cavity. The ribs of the Vulture are more expanded than in _Didus_, especially where they afford the extensive attachment to the epipleurals. But I shall not dwell further on the comparative characters of this part of the skeleton, as more decisive ones of the affinity of _Didus_ are afforded by other parts. In comparing the sternum of the Dodo with that of Doves of flight, the first well-marked difference is in the adaptive development of the keel in the last (Pl. III. fig. 2, _Didunculus_), and in the provision for the concomitantly broader coracoids, the grooves for which meet and run into each other across the fore part of the bone in existing _Columbidæ_ (Pl. XII. fig. 2, _b_); consequently the inner or upper wall of the confluent grooves forms a median prominence (ib. _e_) at the front margin of the sternum, contrasting with the wide notch at that part of the bone in the Dodo (Pl. IV. fig. 4). The next difference, as compared with _Goura_ and most Pigeons, is the absence of the entolateral processes (Pl. XII. fig. 3, _i_) in the Dodo’s sternum: but _Didunculus_ singularly exemplifies its nearer affinity to _Didus_ by a like absence of those processes; only the sternal margins behind the ectolateral processes (ib. fig. 1, _h_), instead of converging with a slight convexity to an obtuse apex, as in Pl. 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 (Pl. XII. fig. 1, _f_), that of other Pigeons two pairs (ib. fig. 3, _f_ _f′_); but the sternum of _Didus_, which is relatively broader, shows no other trace of the anterior notch (Pl. VI. _f_) than is afforded by the rounded angle at which the ectolateral process (_h_) rises from the bone. Although the costal margin is relatively shorter in Doves of flight than in the Dodo, again an intermediate condition is manifested by _Didunculus_ as compared with _Goura_, in which latter Dove there are articular surfaces for three sternal ribs (Pl. XII. fig. 3, _o_ 1, 2, 3), 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 _Didunculus_ there is a pneumatic foramen exterior to the coracoid groove, corresponding with _p_, fig. 4, Pl. 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 _Didunculus_ (Pl. XII. fig. 1).