216 U. 8. P. R. R. EXP. AND SURVEYS ZOOLOGY GENERAL REPORT. 



URSUS, Linn. 



Ursus, LINN-EUS, 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 y^j, premolars ^^, molars ||, = -| = 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 be 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 bone 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 bears 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. 



