OSTEOLOGY OF THE DODO. 61 
(ib. 6’), which gradually rise from the surface of the bone as they extend backward, con- 
verging to form the beginning of the keel about 2 inches from the anterior emargina- 
tion (e): the keel gains a depth of # of an inch at the middle of the sternum, then 
gradually sinks to the level of the bone, as it extends backward, at 14 inch from the 
hind end (Pl. XVIII. fig. 5), a little increasing in thickness as it subsides: its free 
border describes a pretty regular convex curve (Pl. XV.); 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. XXIII. fig. 4). Behind the costal surface (PI. XVIII. c), 
on each side, extends a lamelliform process (Pls. XV. & XVIII. A), 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 XV. ; it answers 
to the ectolateral process (h) of the gallinaceous sternum (Pls. X. & XIV. fig. 3): 
there is no trace of an entolateral process (ib. 7). The thin margin of the Dodo’s breast- 
bone, behind the ectolateral process (Pls. XV. & XVIII. h), is entire and uninterrupted 
to the obtuse apex, and the body of the sternum is imperforate: the notch (f) behind 
the process (i) represents the ectolateral notch of the gallinaceous sternum (Pl. XXIV. 
figs. 1 & 3, f'). The costal border (Pl. XVIII. fig. 2, ¢) 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 (¢ 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)' in advance of these surfaces expands, as it rises upward and a little outward and 
forward, to the extent of nearly an inch; the hinder and outer side is impressed by a 
concavity, continued from the costal border; the inner side is smooth and convex: it is 
not quite entire on either side. The coracoid grooves (Pl. XVI. fig. 4, 2 0') are small 
in proportion to the sternum, and are divided from each other by an interspace of about 
an inch; the outer wall of the groove (4’), 9 lines in extent, is moderately produced and 
convex; it appears to be a continuation of one of the initial ridges (7) of the keel: the 
inner wall of the groove (4) is deeper, and is formed by the obtuse angle of the anterior 
border of the sternum, between the medial and lateral emarginations. External to each 
coracoid groove is a large elliptical pneumatic foramen (p) or depression. There is no epi- 
sternal process. On the convex outer surface of the body of the sternum the “ pectoral ” 
ridge (Pl. XVIII. fig. 1, £)’ is feebly indicated, extending from the outer end of the 
coracoid groove backward and inward to near the posterior third of the keel. The con- 
cave surface of the sternum (ib. fig. 2) shows a number of small pneumatic foramina, 
chiefly along the middle line to near the posterior third. Behind the costal border the 
1 Called “ hyosternal ” in the Geoffroyan determination of parts of the bird’s sternum. 
2 The intermuscular ridges (¢ pectoral,’ ‘subcostal,’ carinal’) are, with other parts of the bird’s sternum, . 
here named as defined in my ‘ Anatomy of Vertebrates,’ vol. iil. pp. 16-23. 
