Of this instructive and determinative bone there are two specimens, the one most entire (Pls. III., IV. fig. 4, & VI.) measuring in a straight line, from the costal process to the hind border, 7 inches. The extreme breadth between the lateral processes (Pl. IV. _h_) is 4½ inches; from this diameter the bone contracts anteriorly to a breadth of 3½ inches at the costal processes (ib. _d_), and posteriorly it contracts more rapidly to an obtuse, horizontally flattened apex (Pl. VI. fig. 3). The anterior border of the sternum (Pl. IV. fig. 4) is widely and rather deeply emarginate at the middle (_e_), less deeply so on each side: the breadth of the mid notch (_b_ _e_ _b_) is 1 inch 9 lines, that of each side notch (_b_ _d_) is 1 inch 2 lines. The sternum is deeply hollowed above (Pl. XI. fig. 4), correspondingly convex beneath (ib.); the keel (_s_) is low and thick, commencing by a pair of broad obtuse ridges (Pls. IV. fig. 4, & VI. fig. 1, _r_ _r_) from the mesial ends of the outer walls of the coracoid grooves (ib. _b′_), which gradually rise from the surface of the bone as they extend backward, converging to form the beginning of the keel about 2 inches from the anterior emargination (_e_): the keel gains a depth of ¾ of an inch at the middle of the sternum, then gradually sinks to the level of the bone, as it extends backward, at 1½ inch from the hind end (Pl. VI. fig. 3), a little increasing in thickness as it subsides: its free border describes a pretty regular convex curve (Pl. III.); it is thick, flat, partially canaliculate: the sides of the base of the keel expand, to be continued gradually into the body of the sternum (Pl. XI. fig. 4). Behind the costal surface (Pl. VI. _c_), on each side, extends a lamelliform process (Pls. III. & VI. _h_), ½ an inch in breadth, upward and a little outward, slightly expanding to its free termination, which, however, is not entire in either specimen: the longitudinal extent of this characteristic process, where it is best preserved, is 1 inch; it is conjecturally restored in Plate III.; it answers to the ectolateral process (_h_) of the gallinaceous sternum (Pls. III. & XII. fig. 3): there is no trace of an entolateral process (ib. _i_). The thin margin of the Dodo’s breast-bone, behind the ectolateral process (Pls. III. & VI. _h_), is entire and uninterrupted to the obtuse apex, and the body of the sternum is imperforate: the notch (_f_) behind the process (_h_) represents the ectolateral notch of the gallinaceous sternum (Pl. XII. figs. 1 & 3, _f_). The costal border (Pl. VI. fig. 2, _c_) is 1 inch 9 lines in extent, and 6 lines across its broadest part; it shows articular surfaces for five sternal ribs, of which the four posterior (2–5) are bilobed, the anterior one (_c_ 1) simple, and limited to the outer half of the border; the second sternum shows some variety in this respect: the deep interspaces, in both, are perforated by pneumatic foramina. The costal process (_d_)[27] in