ARSmOlTlIElilUM. 
7 
from the parietals and sharply defines the upper herder of the temporal fossa. It 
ends some distance in front of the small horns, and its termination may be taken 
as marking the posterior limit of the upper border of the orbit, there being no 
definite postorbital process. The antero-superior portion of the orbital border is 
formed by the frontal ; it is broadly rounded, and at one point near the middle it is 
crossed by a broad shallow depression, which runs upwards and forwards on to the 
side of the base of the horn, where it divides into three or four divergent branches, 
forming deep channels in the bone (PI. I., h.v.). These channels evidently lodged 
blood-vessels which served for the conveyance of blood to or from the covering of the 
horn, and judging from the marked way in which both these vessels and those on 
the anterior face of the horns impress the bone, it seems probable that the covering 
was hard and of much the same nature as that clothing the horn-cores of the 
cavicorn ruminants. 
The lachrymal [1.) is a small bone occupying the anterior angle of the orbit, 
wedged in between the frontal above, and the maxilla, and jugal below. It bears 
a vertically-elongated prominence (see PI. I., 1.) which forms the actual edge of 
the orbit and is connected below with a strong crest borne on the front of the 
maxillary process of the jugal. There seems to be no trace of any lachrymal foramen. 
The nasals (na.) are the most remarkable bones of the skull, and they are enormously 
enlarged, forming almost the whole of the great anterior horns. The sutures between 
these bones and the frontals have already been referred to : they are open only in the 
young (PI. III. figs. 2, 2 a); in the adult or even three-parts-grown animal they are 
completely obliterated (PI. I. and PI. III. figs. 1, 1 a), and the same is the case with 
the suture between the nasals themselves. On the side of the face the ventral border 
of these bones unites first with the upper edge of the maxilla, and in front of this 
with the premaxilla, the suture with which is continued forwards just into the nasal 
cavity. Here a downgrowth of the lower surface of the portion of the nasals forming 
the roof of the nasal cavity unites with a corresponding upgrowth of the maxilla 
which overlaps it (text-fig. 2). The two form a sort of column on either side of the 
posterior face of the nasal cavity, and these columns help to support and form a 
base for the horns. Furthermore, owing to their presence the nasal passage is greatly 
contracted and forms a vertical cleft between them. The roof of the nasal cavity is 
nearly flat and in the adult its edges are thin, sharp, and somewhat everted (PI. I., 
PI. II. fig. 1a): in the young, on the other hand, this edge is wanting (PI. III. 
figs. 2 A, 2 b), so that the nasal roof passes by a gentle curve into the outer face 
of the horn. In the young also the anterior ends of the nasals are free and not 
connected by a bar of bone with the premaxillee. This bar, which is formed only 
at a comparatively advanced age, appears to result from the ossification of the 
anterior edge of a cartilaginous nasal septum, the presence of which is indicated 
by the peculiar groove (PI. III. figs. 1 A, 2 b, ms.y. ; see also text-fig. 2, mes.g) 
