1 38 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 
orbit, of which the jugal forms the whole inferior and most of the anterior 
border ; it has no postorbital process, or even angulation. As a whole, 
the zygomatic arch is long and heavy, though laterally compressed, 
somewhat as in the rhinoceros, and curves out boldly from the side ol 
the skull, enclosing a large temporal opening and forming a very high 
external border for the temporal fossa. A characteristic feature of the 
arch is the steep rise upward and backward to the junction with the 
occipital crest. 
The lachrymal, though not very large, is a very conspicuous bone, 01 
elongate oval shape, ending above and below in a point. It forms the 
dorsal moiety of the anterior border of the orbit and bears a heavy, 
prominent spine ; the foramen is within the rim of the orbit. 
The frontals are short antero-posteriorly, but broad; their hinder ends 
are sharply contracted into narrow processes, which pass between the 
divergent anterior ends of the parietals and bear low, inconspicuous 
temporal ridges, which die away before reaching the orbital border. The 
forehead is broad and is usually plane longitudinally, but may have a 
short, abrupt descent over the orbits (see Lydekker, ’93, PL XIV, fig. 1). 
The postorbital processes are prominent and the frontals extend well out- 
ward to form a roof over the deeply set orbits. Anteriorly, the frontals 
usually have short, triangular nasal processes between the hinder ends of 
the nasal bones, but these processes may be absent (JV. marmoratus) . 
At the postorbital constriction a cross-section shows that the frontals are 
very thick and filled with a dense mass of cancellous bone, but anteriorly 
sinuses appear, extending over the orbits, though these sinuses are com- 
paratively small and cause no protuberance of the forehead. 
The nasals are long, quite broad and strongly convex from side to side, 
curving downward laterally, so that the suture with the maxillary and 
premaxillary is well below the upper contour. In the most abundant 
species, N. imbricatus, the nasals diverge posteriorly and their hinder ends 
are separated by the triangular processes of the frontals, each nasal termi- 
nating in a sharp point. In the much less common N marmoratus , ad- 
mitting that to be a distinct species, the nasals are in contact throughout 
their length and their hinder ends together form a convex curve, which is 
received into a corresponding emargination of the frontals. Anteriorly, 
the nasals have broad, regularly rounded tips and project for a very short 
distance in advance of the premaxillaries. 
