156 PROFESSOR OWEN ON THE GENUS DINORNIS. 
modification of the bone is manifested in D. rheides as in D. robustus (loc. cit. pl. 56. 
fig. 1, 2121’). The malar (26), with which it has coalesced, is remarkable in D. rheides 
(at least I have not found the character in the larger dinornithic crania with the 
zygomatic arch) by the extent of the process sent upward to meet the descending post- 
frontal (12). 
The tympanic bone (figs. 9, 10) shows the single mastoid condyle (e) as in D. robustus, 
D. crassus, and probably all Dinornithes: it is here divided by a low mid-linear ridge at 
the fore part; and the divisions very slightly project behind, on each side a shallow mid 
depression. The stem is subcompressed obliquely from before backward, the hind 
surface inclining rather outward; both outer and inner sides converge to a sharp concave 
posterior margin, the stem becoming thus three-sided with the anterior surface narrower 
than the outer and inner ones. ‘The latter shows a subcircular pneumatic foramen 
(fig. 10) $ inch below the condyle, and not situated in so large and definite a depression 
as in D. robustus (loc. cit. pl. 54. fig. 2,g). The posterior margin shows part of the 
groove and ridge for the attachment of the tympanic membrane. The orbital process (/) 
shows the facet (ps) for the pterapophysis, but not supported on so well-marked a pro- 
minence as in the larger species of Dinornis. The surface for the pterygoid is at the 
fore part of the inner convex condyle (7) for the mandible. The two mandibular surfaces, 
postconcave and preconvex, are similar to those shown in pl. 54. fig. 3, A @, tom. cit. 
External to the mandibular process is the usual subhemispherical cavity (fig. 9, ) for 
the squamosal (fig. 8, 27). 
The mandibular rami coalesce, as in other Dinornithes, by a short symphysis sloping 
from above downward and backward (Pl. XII. fig. 5). Each ramus describes a gentle 
sigmoid curve, best marked at the lower border, which is convex at the hinder, concave 
at the fore half of the mandible (ib. fig. 1, 29-32). 
The back part of each ramus forms an expanded triangular surface (Pl. XII. fig. 6, 29), 
deeply concave from the outer to near the inner side, which is formed by a narrow, 
vertical, convex tract; the vertical ridge or plate of bone extending forward from this 
tract divides the concavity (fig. 7,29) for the insertion of the pterygoid muscles from 
the interarticular depression (fig. 5,7). At the fore part of this depression is the trans- 
versely concave facet for the convex lower condyle of the tympanic. The plate of bone 
extending forward from the outer side of the mandibular base expands and forms along 
its upper part the oblong articular surface (fig. 5,7) adapted to the outer and lower 
condyle of the tympanic. ‘The inner plate, which is sharp above, subsides at the fore 
part of the fossa (4); the surangular part of the ramus (fig. 7, 29) is continued from 
the outer articular surface. The angular piece (fig. 1, 30), smooth and broadly convex 
posteriorly, rapidly contracts to a vertical lamella, which is excavated at the outer part 
of its anterior half for reception of the lower division of the dentary (32), along which 
it is continued internally as a flat thin lamella, below and parallel with the splenial 
(figs. 1 & 7,31), and terminating in a point about an inch from the fore end of the 
