PROFESSOR OWEN ON THE GENUS DINORNIS. 339 
diameter, from the parietal to the basioccipital tuberosity (1’), is 2 inches 3 lines; its 
breadth across the postorbital processes (Pl. LIII. fig. 1, 12) is 5inches. Its length from 
the paroccipitals (ib. 4) to the fore part formed by the coalesced nasals (ib. 15) is 5 inches 
2 lines. 
The flattened end of the nasal process of the premaxillary (ib. fig. 1, 22’) rests 
on a shallow elliptical depression of the nasals (ib. 15), which are confluent with the 
fore part of the frontals (ib. 11). This depression is rounded posteriorly, is 1 inch 
3 lines in length and 1 inch in breadth. The rhinal or olfactory fosse (Pl. LIV. 
fig. 1, m, 14’) are 2 inches 9 lines in length and 2 inches in breadth, divided by a con- 
vex transverse projection of the roof (n') into a larger posterior compartment (n) and a 
smaller and more shallow anterior compartment (14') ; both are subdivided by a low 
median ridge, sharpest and most produced in the posterior compartment. At the back 
and upper part of each lateral division of this compartment are seen the fine, radiating 
grooves diverging from the foramina of the cribriform plate (14). 
The tympanic (Pl. LIII. 28) is a triradiate bone, with short and strong rays, the 
lowest being the broadest and thickest. The mastoid condyle (Pl. LIV. fig. 2, e) of the 
tympanic is 11 lines in long diameter, 3 lines in the short diameter. The stem con- 
tracts transversely, expands in the opposite direction, assuming a trihedral shape, 
widely excavated on the inner facet by the fossa (g), terminating in the large pneu- 
matic canal. The anterior or orbital process (k) is subcompressed, obtuse, 7 lines in 
depth, 10 lines in length; it is impressed, externally, by an oval facet for the ptery- 
goid (pt). The suddenly and largely expanded lower end presents the usual posterior, 
narrow, oblong concavity (ib. fig. 3, 7, h) and the anterior, smaller, but similarly shaped 
convexity (ib. ¢) placed at a right angle to the foregoing. On the outer side of the 
lower end is the usual subcircular, deep depression (Pl. LIII. fig. 2, h), for the 
squamosal element of the zygomatic arch. 
Mandible-—The articular part of the mandible (PI. LIV. fig. 4) is deeply excavated 
between the articular surfaces (i, 7’) which are adapted to those so marked on the 
tympanic (fig. 3). An obtuse angular ridge projects from the inner side of the wall of 
this concavity ; a pneumatic canal perforates its base. The ramus, extended forward 
from the articular end, is divided by two longitudinal fissures into three parts, the 
upper representing the surangular (Pl. LIII. fig. 2, 29’), the lower the angular (30) ; and 
the intermediate portion appears to be the back part of a splenial (31). The surangular 
developes a low convex ridge, with a rough surface external to it, for the insertion of 
the temporal muscles, Its fore part is excavated externally, to be overlapped by the 
upper prong of the dentary element (32'): the angular is more extensively excavated, 
to be overlapped in a similar manner by the lower prong (32”) of the dentary: this 
element had not coalesced with the rest of the mandible, and has been drawn forward 
to show the articular grooves The dentary curves gently down as it approaches the 
thick symphysis, where it coalesces with its fellow to form a broad external symphysial 
2y¥2 
