354 PROFESSOR OWEN ON THE GENUS DINORNIS. 
which the genus was founded, are of a mature bird'; and accordingly I propose to refer 
the bones under description to an Aptornis defossor. 
§ 2. Skull of Aptornis defossor. (Plate XL. figs. 1-3, Plate XLI. figs. 1-4 & 6-8.) 
The skull, as Mr. Taylor remarks, may be said to be massive, the cranial walls are 
thick, much of its osseous substance is compact, and there is the full amount of con- 
fluence of the bones of the head observed in birds. The beak is moderately down-bent, 
and terminated by a transverse subtrenchant margin, in both upper and lower jaws. 
The length of the part of the skull anterior to the orbit exceeds the rest by one-eighth ; 
the fore-and-aft extent of the orbit is rather less than one-fifth that of the entire skull. 
The cranium, viewed either from above or below (Pl. XL. figs. 2 & 3), offers a sub- 
quadrate form. ‘The breadth of the occiput at the paroccipitals (4,4) equals that of the 
cranium at the postfrontals (12,12), a character to which the skull in Notornis and 
Dinornis offers the nearest approach. The occipital region (Pl. XLI. fig. 1) extends 
below the foramen magnum (0) further than above it—a proportion unique in the 
class Aves. 
Those most conversant with the osteological features of birds will best appreciate the 
singular and exceptional characters above defined. The external bony nostrils (Pl. XL. 
fig. 1, n) are large and triangular, or oval-elongate, with the upper, small end almost 
pointed. No groove or furrow is continued forward from them. The interorbital 
septum (ib. fig. 1,0) is entire; the temporal fossa (¢) are deep, though wide apart above 
(ib. fig. 2,7); they are over-arched externally by an upper zygoma (ib. fig. 1, 8-12), 
as in Crocodiles. The cerebral bosses are hardly raised above the level of the inter- 
orbital region (ib. fig. 2, 11). 
The occipital tubercle (Pl. XLI. fig. 1, 1) is hemispheroid, 5 lines in transverse dia- 
meter, feebly impressed by a small pit at the middle of its upper half. The basioccipital 
advancing from the condyle about two lines, then curves downward, and, with the 
basisphenoid, forms a subquadrate almost vertical plate, inclined somewhat forward, 
below, with the lower angles produced and swollen to form a pair of oblong convex 
tuberosities (Pl. XL. fig. 3, /', Pl. XLI. fig. 1, 5,5’). 
The vertical surface of this descending part of the occiput is concave across, but less 
deeply than in Aptornis otidiformis’, the lateral margins not being so produced back- 
ward, especially at their upper part. In both species they form angular lamelliform 
processes, each defending the inner side of the corresponding vagal fossa (ib. fig. 1, »). 
Three minute precondyloid foramina, in a vertical line, range on each side of the base 
of the condyle. The depth of the basioccipitu-sphenoidal (“basilar”) tract, from the 
under part of the condyle to the middle of its under surface, measures | inch 2 lines, to 
* The anchylosis of the stylohyal in the original skull (Trans. Zool. Soc. vol. iii. pl. 52. figs. 3 & 6, 8) indicates 
it to have come from an old bird. 
? Trans. Zool. Soc. vol. iii. pl. 52. fig. 4. 
