GliNEEAL ClIAKACTERS.- 



-MAMMALIA.- 



-General Characters. 



Class L— MAMMALIA. 



In v;batever li'glit wo consiilor the general arrange- 

 niout of the animal kingdom, the Mammalia must 

 alwaj'S oocuiiy the highest place iti 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 would 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 

 tlie whole class, although the great majority of them 

 may come under the denomination of beasts. The 

 term qutulrvpcds, which also applies to the majority, 

 is likewise inadmissible, both because it is equally 

 applicable to many reptiles, and because some true 

 Mammalia arc not furnished with four feet. We are 

 tlierefore 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 

 !iourishing their young, which are born alive, by 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 Sdurfefhiere, or 

 S'icldng av.im.ils, for this class. The term Mammifires, or teat- 

 Ijoarers, is in ordinary use amongst Frenclr writers, and of 

 course refers to tlie same character as the terra Mammalia, liere 

 adopted. The name Pilifares, applied to the class by De Blain- 

 ville, in allusion to tlie hairy covering of most of the species, 

 has never been much made use of. 



wliich they may readily be distinguished from the rest 

 of the Vertebrata. They all breathe air by moans of 

 lungs, consisting of a minutely cellular structure, sus- 

 pended freely in the ca\-ity of the chest, and uncon- 

 nected with any 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 ; tliis 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. 



Tiie 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 uf 

 air-cells, and where these exist, they do not communi- 

 cate with the lungs. Most of the bones are soUd, 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 tire 

 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 great 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 distinguisliable even in the living 

 animal. Li 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 vertebra^, 

 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 fo' 

 the reception of the brain, is of larger comparative size 

 in these tlian in any other Vertebrata ; its bones are 

 immovably connected 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 row along their 



