MAMMALIA. 
3 
The species of the Mammalia vary in their forms according to 
the uses which the animals have to make of them. Nearly all 
of the Mammalia have four limbs. The Cetacea have no abdominal 
members, and their anterior members are formed like fins or 
paddles for swimming. 
The organs of sense are generally more developed in this class of 
animals than in all those we have hitherto studied. The sense of 
touch, which is almost wanting in some — as the Horse and the Ox 
— because their extremities are covered by hoofs, is very highly 
developed in Monkeys. With these animals, the upper member is 
terminated by an organ of prehension, which can in a manner 
mould itself on the objects it takes hold of, and which imparts to 
the sense of touch an enhanced delicacy. The sense of vision alone 
is highest in the class of Birds. 
The seeing apparatus is, in general, more developed in the 
Mammalia that prowl by night, than in those which seek their 
food by day. Some which, like the Moles, live underground, have 
excessively small eyes, over which the skin is merely attenuated in 
certain species of Mole, there being no visual aperture whatever. 
Yery highly developed in carnivorous animals, the sense of 
smell is generally less developed in the other classes of Mammalia. 
It is acute in the Buminantia and in the Solipedes. 
The more timid and the weaker the animal, the finer is its sense 
of hearing. This sense, moreover, undergoes great variations in 
the Mammalia. In aquatic Mammalia, it is comparatively dull, 
with some exceptions (p. 35). 
The taste differs equally, according as the Mammalia are her- 
bivorous, insectivorous, or carnivorous. 
The muscular system depends on the form and manner of loco- 
motion and on the length of the animal. 
The nervous system among the animals of this class only differs 
by having certain of its anatomical elements more or less developed. 
In general, the brain is sufficiently voluminous, and increases in 
size in proportion as the animal rises in the organic scale.. 
The functions of nutrition are performed in the same manner in 
nearly all the Ma mm alia ; so that the digestive organs vary but 
very little in this great class. 
The upper orifice of the digestive tube, or the mouth , is mostly 
provided with teeth, the form of which depends on the food upon 
b 2 
