Page:The American Cyclopædia (1879) Volume XI.djvu/83

 MAMMALIA 75 (1868) ; and Teoria della religione e dello state, e del suoi rapporti speciali con Roma e colle oni cattoliche (1868). He also contrib- utes largely to the philosophical review La losqfia delle Scuole italiane. MAMMALIA, the highest vertebrated animals, eluding man, warm-blooded, breathing by gs separated from the abdominal cavity by diaphragm, generally covered with hair, and nging forth their young alive, which they ourish by the secretion of mammary glands whence their name). Most mammals are corn- only known as quadrupeds, from their hav- f our feet suited for progression on a solid rf ace ; but the terms are not synonymous, as st reptiles are four-footed, and the whales ,nnot be called quadrupeds. The form of animals is very various ; among them we see an walking erect, the flying bats, the swim- ing cetaceans, the bulky elephant, the slow- iving sloth, and the agile squirrel ; yet the ree regions of head, neck, and trunk can al- ways be recognized in the skeleton, and gen- illy in the living animal. The neck, though rying in length, from that of man (one sev- th of the spinal column) to that of the giraffe (three sevenths), with two or three exceptions, consists of 7" vertebras ; some of the sloths have 8 or 9, and some manatees are said to have 6 only ; in the hoofed animals the length of the neck depends on that of the fore legs, for the purpose of grazing ; but the elephant has a long proboscis to compensate for the shortness of the neck rendered necessary by the ponderous head ; the extra vertebras of the sloths are by some considered as dorsals with rudimentary ribs to give additional mobility to the neck. The number of dorsal vertebras va- ries from 11 in some of the bats to 22 in some of the sloths, man having 12 ; the lumbar ver- tebras, 5 in man, are 2 in the ornithorhynchus and 9 in some lemurs, stronger than the dor- sals, and without ribs, which are replaced by long transverse processes ; the sacral vertebras, usually 4, vary from 1 to 9 ; the rudimentary tail of man, the os coccygis, consists of 4 bones, but in the long-tailed manis there are 46 cau- dal vertebras. The skull is articulated to the spine by two occipital condyles, which permit the upward and downward motions of the head, the lateral and rotating movements de- pending on the articulation between the first and second vertebras ; in whales the short neck is immovable as in fishes, and its bones are very thin and more or less consolidated to- gether ; the strong ligamentum nuchce, which supports the head, is attached to the spinous processes and skull. The caudal vertebras are of two kinds, one having a spinal canal, the other not, and the processes are always devel- oped in accordance with the use made of the tail ; in most mammals its movements are con- fined to brushing away insects from the skin, but in the kangaroo it forms with the hind legs a firm tripod from which the animal Kprings, and in some South American monkeys it is prehensile and used as a fifth hand in hanging from trees ; in the whales it becomes a powerful swimming organ, is provided on its under surface with V-shaped bones for the protection of the blood vessels, and, being horizontal, is used principally as an organ by which to rise to the surface to breathe ; in the beaver the transverse processes and the lower spinous are very large for the attachment of the muscles, which move the tail like a trowel chiefly in a downward direction. The bones of the spine are united by elastic fibro-cartila- ges ; these, in whales, form osseous disks, sep- arating on maceration, and frequently used by arctic travellers for plates. As all mammals breathe air, the mechanism of their respiration depends on the movable ribs and the dia- phragm ; man has 7 true and 5 false ribs, the former united to the sternum, the latter not ; the number is in proportion to that of the dor- sal vertebras ; in the whale, of 12 ribs, 11 are false, in the unau 11 out of 23, in the horse 8 out of 18, in the cats 4 out of 13, and in the manatee 14 out of 16 ; in the carnivora they are dense and narrow, in the herbivora large, broad, and thick. The breast bone varies in shape according to the presence or absence of clav- icles; in non-claviculated mammals the chest is compressed laterally, and the breast bone has a projecting keel as in birds ; in bats it is much keeled, in the higher apes flat as in man, and in the moles it extends in front of the ribs, forming a distinct piece ; in mammals with clav- icles the chest approaches very nearly to that of man ; the human chest, however, is the only one in which the transverse exceeds the antero- posterior diameter, causing the greater separa- tion of the shoulders and the increased facility of movement of the arms. The anterior ribs always extend as far as the breast bone, and are thus true ribs, differing in this respect from those of birds. Each of the ribs is usually connected by its head to an articular cavity formed by the bodies of two vertebras, and by its tubercle to the transverse process of the posterior of the two ; in the monotremata they are connected with the body alone, and in ceta- ceans often only with the transverse processes. The breast bone consists of several pieces, one behind the other, to which the anterior or true ribs are joined by cartilages which rarely be- come ossified ; the posterior are the false or floating ribs, and are not attached immediately to the breast bone ; this arrangement gives mo- bility to the chest and allows the elevation and depression of the ribs during respiration. The bones of the skull and face are immovably connected with each other, a character which does not occur in any of the lower classes ; the brain cavity is larger than in birds and rep- tiles ; the occipital condyles, near the centre of the base in man, are gradually removed to the posterior portion as we descend in the scale; the number of cranial bones, eight in man, is less than in most lower vertebrates. For the general characters see COMPARATIVE ANATOMY,