116 PROFESSOR OWEN ON THE GENUS DINORNIS. 
inner ' concavity (fig. 1) is limited to the fore part of the disk, and is due chiefly to the 
upward or backward bending of the anterior border, slightly deepened by the ill-defined 
pneumatic fosse (ib. pn pn) near the costal border (cc). As the sternum recedes 
backward the inner concavity changes to a convexity, both lengthwise and transversely, 
the broad mesial process (ib. g) rising into a low obtuse ridge (ib. 7) along the mid- 
line of the inner surface. 
The outer surface of the bone offers a corresponding convexity at the fore part, and 
concavity both lengthwise and across in the rest of its extent; and this concavity is con- 
tinued along part of the origins of the lateral processes. The thickness, or rather 
thinness, of this flattened sternum varies from + to $ and 315 of an inch. 
The costal border is traversed by two oblique parallel articular ridges (fig. 2, mn), 
with shallow intervening and contiguous depressions (ib.000). The lateral process (h) 
retains, anteriorly or externally, the thickness of the lower part of the costal tract, 
diminishing in thickness towards the posterior border, which there has a breadth of 
6 lines; the inner or posterior surface of the process is impressed by a shallow groove 
lengthwise, and, after an extent of about 3 inches from the sternal body, the process 
appears to be twisted upon itself from before backwards, the inner border of the outer 
surface becoming the inner ridge-like border of the process itself, which is then com- 
pressed from without inwards, instead of from before backwards as at its basal half. 
This twist is more notable in the right process (4) than in the left one (h'), a greater 
proportion of which is preserved. Dimensions of different parts of this sternum are 
given in the Table of Admeasurements, p. 122. 
Sternum of Dinornis rheides. (Plates VIII. & IX.) 
The sternum of Dinornis rheides is of the long and slender type, with the minor 
degree of divergence of the lateral processes. The body of the sternum is cleft for 
more than half its extent by a pair of posterior notches (f/f) of a narrow angular form 
with the apex rounded off, leaving a long and narrow mesial process (7), which, in the 
specimen described, is notched at its rounded extremity, and has a small unossified 
vacuity about an inch anterior thereto. ‘The entire part of the sternal body is mode- 
rately convex in every direction externally (Pl. VIII.), and correspondingly concave 
within (Pl. [X.). On the inner surface it is impressed by two special deeper hollows 
(Pl. LX. 2) just behind the anterior border and near the base of the costal processes 
(dd): these pneumatic depressions are perforated by several small foramina conveying 
air from the air-cells which occupied them into the cancellous texture of the thicker 
parts of the sternum. Neither the Ostrich nor Cassowary shows such pneumatic 
* In the following descriptions I term the surface of the sternum which, in its natural position, is upward, 
or toward the cavity of the body, internal or ‘‘inner”’ surface; the opposite one, which looks downward and is 
toward the pectoral muscles, I call the external or “ outer’’ surface. 
