282 THE OSTEOLOGY OF ELOTHERIUM. 
cies in which these jugal plates are found. Nothing is known concerning their presence 
or absence in the European representatives of the genus. Leidy’s material gave him no 
reason to suspect their occurrence in the species described by him, and he consequently 
restored the zygomatic arches without them (769, Pl. XVI). Marsh first discovered the 
processes in a skull of the species named by him /. crasswm, and it has sometimes been 
assumed that they were more particularly characteristic of that form. As a matter of 
fact, they have been observed in all of the American species of which well-preserved 
skulls are known, viz., 2. mortoni, EL. ingens, and E. imperator, and, in all probability, 
all the American forms, at least, possessed them. 
The achrymal is a rather large bone and forms nearly half of the anterior boundary 
of the orbit. On the face it is expanded into quite a large plate, which articulates below 
with the jugal, in front with the maxillary, and above with the frontal, the long anterior 
process of which prevents any contact between the lachrymal and nasal. In Aippopota- 
mus the very short, broad frontal has no anterior process, and so the nasal and lachrymal 
are connected, as they are also in Sus. Within the orbit the lachrymal is but little 
extended ; the foramen is single, very small, and placed inside the orbital margin. The 
lachrymal spine is very low. 
The nasals are narrow, slender and very much elongated. Their greatest width is 
at the anterior end of the nasal processes of the frontal, and here is also their greatest 
transverse convexity ; ‘from this point they narrow and flatten, both in front and 
behind. Anteriorly they contract very gradually and terminate in sharp points, with 
their free ends quite deeply notched. In /. wmgens the nasals appear to be relatively 
shorter than in the other species. In /Hippopotamus these bones have much the same 
shape as in Hlotherium, but they narrow more abruptly behind the poit of greatest 
width, and their free ends are not notched. In Sus the nasals are truncated posteriorly 
and in front their free tips project far beyond the borders of the premaxillaries. 
The premaxillaries ave very large and heavy bones, the horizontal or alveolar portion 
especially so. Posteriorly, this portion is constricted, forming a groove for the reception 
of the lower canine, expanding again in front to carry the large incisors. The palatine 
processes are not much developed, the very large incisive foramina leaving but little 
space for them; the spines are long and slender, extending behind the canine alveolus. 
The ascending ramus of the premaxillary is low and rises gradually behind, and though 
broad at first, it rapidly becomes very slender, terminating behind in a fine point. 
Though these bones in Hlotheriwm haye a very different appearance from the immensely 
enlarged premaxillaries of Hippopotamus, yet both may have been formed by divergent 
modifications of a common plan. 
The maxillary is greatly extended antero-posteriorly, in correspondence with the 
