MAMMALIA. 455 
the ground. The body is covered with a coat of long, dense hairs. The 
tail is extremely short. Musk oxen are found in the greatest numbers 
within the Arctie circle; considerable herds are occasionally seen near the 
coast of Hudson’s Bay. The horns of the musk ox are employed for 
various purposes by the Indians and Hsquimaux, especially for making cups 
and spoons. From the long hairs growing on the neck and chest, the 
Ksquimaux make a kind of wig drooping down to the shoulders, to defend 
their faces from troublesome insects. 
A fossil species (B. pallasii), which seems to be related to the musk ox, 
has been discovered in the States of Kentucky and Missouri, and we are 
told also, in Siberia. Whether these remains are perfectly identical is still 
to be ascertained. ) 
Group 5. Rodentia. 
The group of Rodentia includes those herbivorous mammals whose jaws 
are provided in front with long, curved, and cylindrical or nearly cylin- 
drical teeth, the exposed ends of which are bevelled off on the inner surface, 
so that they terminate in a sharp, cutting edge. These teeth, two in 
number in each jaw, and sometimes four’in the upper, are separated by a 
wide empty space from the molars, and thus cannot seize a living prey, nor 
tear any flesh; they cannot even cut the food, but serve to file, and by 
continued action they reduce it into separate molecules; in a word, they 
gnaw: hence the term Rodentia or gnawers. The moiars have a flat 
<rown, whose enamelled eminences are always transverse, and studded 
‘with blunt and but litile elevated tubercles. When these eminences are 
simple lines, and the crown is very flat, the genera are more exclusively 
frugivorous; when the eminences are divided into blunt tubercles, they 
are omnivorous. The condyle of the lower jaw is longitudinal or rounded, 
and inclosed in the glenoid cavity in such a manner as to permit very little 
lateral motion to the jaw, which, however, moves freely in the longitudinal 
direction. This group, one of the most clearly defined, has representatives 
in all parts of the world, the species of which are very numerous, feeding 
upon vegetable substances, and generally of small size, a few exceeding the 
common rabbit in bulk. The form of the body is generally such that the 
hinder parts of it exceed those of the front, so that they rather leap than 
walk. In some of them this disproportion is even as excessive as it is in 
the kangaroo. 
Fam. 1. Leporip#. The hare family is less numerous in species than 
other families of rodents, and offers many exceptions to the general or nor- 
mal characters of the order. The large size of the openings in the skull, 
combined with the very imperfect condition of the palate; the perforations 
in the nasal process of the superior maxillary bone; large orbits meeting in 
the mesial line of the cranium ; the small temporal fossze ; and the increased 
number of incisors and molar teeth, are among the more striking characters 
presented by the skull. The extra pair of incisors in the upper jaw is 
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