216 
U. S. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
URSUS, Linn. 
Ursws, Linnaeus, Systema Naturae, 1735. 
Gen. Ch.— Body thick, clumsy, and large. Feet entirely plantigrade; soles naked; nails long. Tail very short. Head very 
broad. Dentition: incisors canines premolars molars |5§, = ~ = 42. 
The above brief characters will serve to distinguish one of the best defined groups in the 
animal kingdom. The species are not numerous, nor are they to he found, except in the tempe¬ 
rate regions of the northern hemisphere. A single species, U. ornatus, is found in the South 
American Andes. North America possesses more species than any other part of the world, 
having at least four, and perhaps five. 
The skull of the bears is longer, and the muzzle longer and broader than in the dogs and 
cats. The orbital processes of the frontal hone are moderately developed, almost wanting in 
the very young. The intermaxillary comes into absolute contact with the frontal bone. The 
bony palate extends considerably behind the molar teeth. The lower jaw is massive and very 
high ; the coronoid process subtriangular, and as long as high. 
The dental formula of the hears is the same as in the majority of the Canidae, the molar 
teeth in the lower jaw attaining the maximum (seven) found in the placental mammals. It is 
very seldom, however, that the full number is met with, owing to the deciduous character of 
some of the premolars, which are very small. Indeed, in most American species, one or two 
of these on each side, above and below, are usually wanting, their place indicated by a small 
socket, which is sometimes obliterated entirely, and only a sharp bony ridge occupying its place. 
The second premolar of both jaws disappears, and then the third; the' fourth is almost always 
retained, and usually the first also, which is situated very close to the canines, and generally 
incumbent upon them. The first three premolars above and below are very small and have but 
a single root; their crowns are occupied by a single compressed tubercle. The fourth tooth in 
both jaws is a premolar, but is much larger than those in front of it; the upper has three fangs, 
the lower two. The first upper molar has three roots, the second four ; the first, second, and 
third molars have two each ; those of the third connate. 
The fourth upper premolar represents the sectorial tooth of the carnivora, but is here greatly 
reduced from its formidable homologue in the dogs ; its shape is triangular, but the base of the 
triangle is posterior instead of anterior. The first true molar above has an oblong crown, with 
four principal cusps, and sundry supplementary wrinkles or irregularities. The second or pos¬ 
terior molar is the longest of all, and is shaped somewhat like the first molar, with an additional 
portion on the posterior extremity, usually subtriangular, and without prominent tubercles. In 
the lower jaw, the fourth lower premolar is smaller and narrower than the upper one. The 
first true molar is long and narrow, especially anteriorly ; it still retains some of the charac¬ 
teristics of the same tooth in the Canidae , especially when viewed laterally. The second molar 
comes nearest the first true molar above, but is narrower ; the third molar is rounded or elon¬ 
gated, as broad as the second molar, but shorter ; its variations in comparative size furnish 
excellent specific characters. 
The inner line of the upper molars is straight, and those of opposite sides parallel. In both 
upper and lower jaws, the exterior and interior outlines of each row of molars are straight and 
converge anteriorly, so that the teeth narrow as we proceed forwards. 
