56 
UPPER MAMMAL GALLERY. 
species, such as the Squirrels, in which the £ore-limhs are used 
tor grasping or climbing ; while they are incomplete or absent 
in those which live a simple terrestrial life, and use their fore- 
limbs for walking or digging only. 
The lower jaw is attached to the skull by a longitudinal 
condyle, which gives a large amount of mobility and freedom 
at a corresponding sacrifice of strength and rigidity. This 
Fig-, 32. 
Skeleton of a Squirrel. 
c, carpus ; cd, caudal vertebrae ; cl, clavicle ; cv, cervical vertebrae ; d, dorsal 
vertebrae ; fb, fibula ; fm, femur ; h, humerus ; I, lumbar vertebrae ; 
me, metacarpus ; mt, metatarsus ; ph, phalanges ; pelvis ; i', radius ; 
s, sacral vertebrae ; sc, scapula ; sk, skull ; th, tibia ; tarsus ; u, ulna. 
permits of the backward-and-forward movements so noticeable 
in a Rabbit when feeding. 
Rodents, next to Bats, are the most widely spread of all 
Mammals, extending over the whole world, with the exception 
of the more remote Pacific islands, to which they have never 
had access. Many of the species are arboreal, like the Squirrels, 
or aquatic, like the Water-Rat and Musquash; but the great 
majority are burrowing and terrestrial animals, which only come 
forth by night to seek their food, so that, altliough so numerous, 
they are little seen by ordinary observers. 
