290 PROF. OWEN ON THE ANATOMY 
rower to the last. The bony appendages to the vertebral ribs are developed in the 
second to the eighth inclusive: they are articulated by a broad base to a fissure in the 
posterior margin of these vertebral ribs a little below their middle part; those belonging 
to the third, fourth, fifth, and sixth ribs are the longest, and overlap the succeeding rib : 
these processes are not anchylosed in the specimen described. The Rhea comes nearest 
to the Apterya in the size of these costal appendages. The first four sternal ribs are 
transversely expanded at their sternal extremities, which severally present a concave 
surface lined with smooth cartilage and synovial membrane, and playing upon a corre- 
sponding smooth convexity in the costal margin of the sternum, which thus presents 
four true enarthrodial joints with capsular ligaments on each side. This elaborate struc- 
ture is not, however, peculiar to the Apteryx among birds, but relates to the importance 
of the movements of the sternal ribs, which are the centres upon which the respiratory 
motions hinge,—the angles between the vertebral and sternal ribs, and between these 
and the sternwm, becoming more open in inspiration when the sternum is depressed, and 
the contrary when the sternum is approximated to the dorsal region in expiration. 
The sternum—the main characteristic of the skeleton of the bird—is reduced to its 
lowest grade of development in the Apteryx. In its small size, and in the total absence 
ofa keel, it resembles that of the Struthious birds, but differs in the presence of two 
subcircular perforations on each side of the middle line, in the wide anterior emargina- 
tions, and in the much greater extent of the two posterior fissures. 
The anterior margin presents no trace of a manubrial process as in the Ostrich: on 
the contrary, the wide interspace between the articular cavities of the coracoid is deeply 
concave: in the extent of this interspace the Rhea most resembles the Apteryx, but its 
contour is almost straight ; in the Cassowary the space is narrower but is deeply notched. 
The articular surface for the coracoid is an open groove, which in the fresh state is co- 
vered with articular cartilage : external to this groove the anterior angles of the sternum 
are produced into two strong triangular processes with the apex obtuse. The costal 
margin is thickened, and when viewed anteriorly, presents an undulating contour, from 
the presence of the four articular convexities for the sternal ribs and the intermediate 
excavations. The sternum of the Emeu presents a similar appearance. ‘The breadth of 
each sternal perforation is nearly equal to that of the intervening osseous space ; in the 
specimen described they were not quite symmetrical in position. The extent of the 
posterior notches is equal to one half the entire length of the sternum: the external 
boundaries of these notches curve towards each other: there is also a slight want of 
symmetry in the form, position, and extent of these notches, as may be seen in the 
figures (Pl. LV. Fig. 2 & 3.) 
The scapula and coracoid are anchylosed': a small perforation anterior to the articular 
surface of the humerus indicates the separation between the coracoid and rudimental 
clavicle, of which there is otherwise not the least trace. 
1 Pl. LV. fig. 4. 
