Animals that suckle their young by means of lactiferous teats. In external and internal structure they resemble man: most of them are quadrupeds; and with man, their natural enemy, inhabit the surface of the Earth. The largest, though fewest in number, inhabit the ocean.
Linnaeus divided the mammals based on the number, situation, and structure of their teeth; mammals have the following characteristics:
Heart: two auricles, 2 ventricles. Warm, dark red blood;
Lungs: respires alternately;
Jaw: incombent, covered. Teeth usually within jaw;
Teats: lactiferous;
Organs of sense: tongue, nostrils, eyes, ears, and papillae of the skin;
Covering: hair, which is scanty in warm climates, hardly any on aquatics;
Supports: four feet, except in aquatics; and in most a tail. Walks on the Earth and speaks.[2]
Primates have four cutting upper parallel fore-teeth, except in some bat species which have two or none; solitary tusks in each jaw, one on each side; two pectoral
teats; two feet and hands; flattened, oval nails; and they eat fruits.[2]
Ferae usually have six conic fore-teeth in each jaw, longer tusks, grinders with conic projections, feet with subulate
claws, and feed on carcasses and prey on other animals.[2]
Glires have two cutting fore-teeth in each jaw, but no tusks, feet with claws formed for running and bounding, and eat bark, roots, and vegetables, which they gnaw.[2]
Pecora do not have upper, not many lower cutting fore-teeth, hoofed, cloven feet, and feed on herbs which they pluck, chewing the cud; four stomachs, a paunch for macerating and ruminating food, a bonnet for reticulating and receiving it, an omasus or maniplies of numerous folds for digesting it, and an abomasus or caille, fasciate, for giving it acescency and preventing putrefaction.[2]
Cete have some cartilaginous, some bony teeth, no nostrils but a fistulous opening in the anterior and upper part of the head, pectoral fins instead of feet, horizontal, flattened tails, no claws, live in the ocean, and feed on mollusca and fish.[2]
^Linnaeus, C. (1758).
"Classis I. Mammalia". Systema naturae per regna tria naturae: secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Vol. 1 (Tenth reformed ed.). Holmiae: Laurentii Salvii. p. 14−77.
^
abcdefghijTurton, W. (1806).
"Class I. Mammalia". A general system of nature: through the three grand kingdoms of animals, vegetables, and minerals, systematically divided into their several classes, orders, genera, species, and varieties. Translated from Gmelin. Volume 1. London: Lackington, Allen, and Co. pp. 5−130.
^Ord, G.; Rhoads, S. N. (1894).
"Fair squirrel Sciurus flavus". A reprint of the North American zoology by George Ord. Haddonsfield, New Jersey: Samuel N. Rhoads. p. 20.