General Characters. ^MAMMALIA. General Characters. 3 
Class L— MAMMALIA. 
In -wliatever liglit we consider the general arrange- 
ment of the animal kingdom, the Mammalia must 
always occupy the highest place in the system. Both 
in complexity of organization and in general intelli- 
gence, the members of this class, which even includes 
our own species, bear the palm from all other animals ; 
and, if we descend to purely utilitarian views, it is 
amongst the ranks of the Mammalia that we must seek 
for all the most valuable of those creatures which have 
been in every age most serviceable to the human race, 
and have contributed most importantly to the progress 
of civilization. The noble and generous horse, who 
lends his back to the burden and his neck to the yoke 
with equal readiness ; the brave and faithful dog, the 
constant friend and companion of man in all countries, 
and his firm ally in the subjugation of other animals ; 
the camel, the far-famed “ ship of the desert,” without 
whose patient endurance and great strength the vast 
sandy plains of Africa and the desert steppes of central 
Asia, would have presented a more serious obstacle 
than even the ocean itself to the intercourse of the 
eastern nations ; the cattle and sheep which constitute 
the riches of pastoral tribes, and without which an 
advanced civilization woidd be almost an impossibility: 
these are only a few of the important species of the 
class Mammalia, which have been in all times subjected 
to the dominion of man. We may seek in vain in any 
other class of animals for even a single species that 
may be compared with one of these. 
Notwithstanding the great importance of the Mam- 
malia, however, we have no English word to express 
the whole class, although the great majority of them 
may come under the denomination of beasts. The 
term quadrupeds, which also applies to the majority, 
is likewise inadmissible, both because it is equally 
applicable to many reptiles, and because some true 
Mammalia are not furnished with four feet. We are 
therefore reduced to the employment of the term mam- 
mals, to express the animals now under consideration 
in a general sense ; as this term, derived from the 
Latin word mamma, a breast or teat, expresses the 
leading peculiarity by which these creatures are dis- 
tinguished from all other animals — namely, that of 
nourishing their young, which are born alive, bj'^ means 
of a secretion produced by certain glands placed on the 
chest or abdomen of the mother.* 
Independently of the physiological characters derived 
from the viviparous reproduction and the provision of 
milk for the nourishment of the young, which prevail 
in all the animals of this class, we find in other points 
of their structure an abundance of peculiarities by 
* The Germans have the expressive term 8avgethiere, or 
sucking animals, for this class. The term Mammiferes, or teat- 
hearers, is in ordinary use amongst French writers, and of 
course refers to the same character as the term Mammalia here 
adopted. The name PUiferes, applied to the class by De Blain- 
ville, in allusion to the hairy covering of most of the species, 
has never been much made use of. 
which they may readily he distinguished from the rest 
of the Vertebrata. They all breathe air by means of 
lungs, consisting of a minutely cellular structure, sus- 
pended freely in the cavity of the chest, and uncon- 
nected with an}’' air-tubes or sacs penetrating the other 
organs of the body, as in Birds. The chest is separated 
from the abdominal cavity by a muscular and ten- 
dinous partition called the diaphragm, the movement of 
which, by enlarging the cavity of the chest, is one 
principal cause of the inspiration of air. The heart 
contains four cavities, two ventricles for the propulsion 
of the blood through the arteries, and two auricles for 
its reception from the veins ; this character is common 
to the Mammalia and Birds. The mouth is closed by 
fleshy lips, which are almost always movable ; and the 
skin, with but few exceptions, is more or less covered 
with hair. 
The structure of the skeleton also furnishes most 
important characters in this, as in other classes of ver- 
tebrata. The bones are, for the most part, destitute of 
air-cells, and where these exist, they do not communi- 
cate with the lungs. Most of the bones are solid, and 
those which possess cavities (such as the thigh-bones 
and arm-bones) have them filled with a peculiar fatty 
substance, well known as marrow. Air cavities in the 
bones are usually confined to the head, where they are 
commonly known as sinuses ; these attain a great deve- 
lopment in the ruminating quadrupeds, such as the 
sheep and deer, and in the elephant the gi'eat size of 
the skull is mainly due to the large air-cells which 
separate the two faces of the cranial bones. 
The body of a mammal is usually divided into three 
portions — the head, neck, and trunk ; and these are, in 
most cases, clearly distinguishable even in the living 
animal. In the skeleton, as will be seen by a glance 
at plates 32, 33, 34, they are still more strongly marked, 
and we find that in this we may again divide the bones 
of the trunk into several distinct systems — namely, the 
dorsal vertebrae, with the ribs ; the lumbar vertebrae, 
forming the loins ; and the sacrum, bearing the sup- 
porting arch of the hinder extremities ; beyond which 
the vertebral column is usually continued into a gra- 
dually decreasing series of vertebrae, forming the tail. 
The skull, including all the bones of the head, pre- 
sents the following leading characters in mammals : — 
The cranium, or true skull, containing the cavity for 
the reception of the brain, is of larger comparative size 
in these than in any other Vertebrata; its bones are 
immovably conneeted with each other, and with those 
of the upper jaw and face, a character which is pecu- 
liar to these animals. The occipital bone, which forms 
the base of the skull, and is perforated by the large 
aperture for the passage of the spinal cord, bears a 
pair of articulating tubercles by which the skull is 
attached to the first vertebra of the neck. The upper 
jaw is formed by two maxillary and two intermaxillary 
bones, which bear teeth in a single low along their 
