PROFESSOR OWEN ON THE GENUS DINORNIS. 359 
they extend forward into a horizontal plate half an inch broad (fig. 3,22”); it is slightly 
concave, with an irregular surface below, more concave and smooth above; it has a 
thickish, smooth median margin, and a rough outer one rapidly rising as it advances to 
be continued into the nasal branch of the premaxillary. 
The anterior part or “ body” of the bone (Pl. XL. figs. 1 & 2,22) is 2 inches 9 lines in 
length, 1 inch 3 lines in breadth at the base, whence the branches radiate, thence tapering 
to an anterior, depressed, slightly rounded terminal trenchant edge half an inch broad. 
The upper surface for about an inch from this end is smooth; each lateral margin is 
rough, and gains in thickness as it recedes, forming a convex, non-canaliculate dentary 
border, 2 inches 5 lines long, about 1} line thick, continued, contracting, for about 
6 lines, upon that of the maxillary. The rough surface gradually extends upon the 
outer side of the premaxillary to a breadth of 3} lines, where it is arrested by a very 
shallow smooth impression, above which open six or eight conspicuous nervo-vascular 
foramina in an irregular longitudinal series. Here the sides of the premaxillary are 
more rapidly continued into the upper surface; the arch or transverse convexity not 
being a regular curve. 
The palatal surface of the premaxillary (ib. fig. 3, 22’) is concave lengthwise, but more 
so across, especially midway between the fore and hind end of such surface. It is divided 
lengthwise into three tracts—one median, becoming concave and smooth at its posterior 
half, and two lateral, similarly concave, but irregular of surface. They deepen forward 
into narrow grooves, from which nervo-vascular canals pass into the substance of the 
bone ; and the grooves grow more shallow as they extend to the almost trenchant termi- 
nation of the upper beak. The fore part of the common midpalatal vacuity is half an 
inch in advance of the fore part of the outer bony nostril; and the ridge from the upper 
mid tract of the premaxillary part of the roof of the mouth extends half an inch in 
advance of the palatal vacuity before it rises to the upper plate of the premaxillary. 
The vacuity of the premaxillary, which is an anterior extension of the common nasal 
cavity, becomes divided only along the anterior half of the outwardly seeming solid part 
of the premaxillary. From the apices of the long conical cavities, so separated and 
extended toward the fore end of the upper beak, one or two canals are continued out- 
ward, forming by their termination the anterior of the conspicuous nervo-vascular canals 
above noted. ‘The nasal branch (22'), 2 inches 8 lines in length, gradually loses breadth 
as it recedes, viz. from 11 lines to 7 lines between the bifurcating part of the nasals, 
then more rapidly to its cranial termination, which is nevertheless broadly rounded, 
where it overlies the smooth and free prefrontal, coalescing by its periphery with the 
frontals and nasals. The premaxillary processes of the latter underlap the premaxillary, 
the margins of which appear thickened by bending down to the nasal coalescence; the 
under surface of the internarial part of the premaxillary is reticulate. This part of the 
long arch of the base of the beak is strengthened by the pair of longitudinal ridges due 
to the produced premaxillary processes of the nasals. 
