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Show 38 ANIMALIA VERTEBRATA. CLASS I. MAMMALIA. 1. e placed at the head of the animal kingdom, The mamma Ia ar . b 1 't ·s the class to which man himself e ongs, not only because I I but also b ecause I't I·s that which en1~ oys the mos.t numerous faculties, the most delicate sensations, the most. :aried powers f . d 'n which all the different qualities seem com· o motiOn, an I f . lli bined in order to produce a more perfect degree o I.nte . gence, the one most fertile in resources, most susceptible of perfection, and least the slave of instinct. As their quantity of respiration is moderate, ~hey ~re de· signed in general for walking on the earth, but ":Ith VIgoro~ and continued steps. The forms of the articulatiO~S of their skeleton, are, consequently, strictly defined, wh~c.h deter· mines all their motions with the most rigorous preciSIOn. Some of them, however, by means of limbs consid~rably elongated, and extended membranes, raise themselves m ~h: air· others have them so shortened, that they can move Wit facility in water only, though this does not deprive them of the general characters of the class. The upper jaw, in all of these animals, is fixed to the era· nium • the lower is formed of two pieces only, articulated by a proje~ting condyle to a :fixed .temporal bone; the ne~k con· sists of seven vertebrre, one single species excepted which has nine· the anterior ribs are attached before, by cartilage, t~ a ster;um consisting of several vertical pieces; their amenu1 .,. extremity commences in a shoulder-blade, that is ~ot lated, but simply suspended in the :flesh, often restmg o~ sternum by means of an intermediate bone, called a clavicle. MAMMALIA. 39 This extremity is continued by an arm, a fore-arm, and a hand, the latter being composed of two ranges of small bones called the carpus, of another range called the metacarpus, and of the fingers, each of which consists of two or three bones, termed phalanges. With the exception of the cetacea, the first part of the posterior extremity, in all animals of this class, is fixed to the spine, forming a girdle or pelvis, which, in youth, consists of three pairs of bones, the ilium which is attached to the spine, the pubis which forms the anterior part of the girdle, and the ischium, the posterior. At the point of union of these three bones is situated the cavity with which the thigh is articulated, to which, in its turn, is attached the leg, formed of two bones, the tibia and fibula; this extremity is terminated by parts similar to those of the hand, i. e. by a tarsus, metatarsus and toes. The head of the mammalia is always articulated by two condyles, with the atlas, the first vertebra of the neck. The brain is always composed of two hemispheres, united by a medullary layer, called the corpus callosum, containing the ventricles, and enveloping four pairs of tubercles, named the corpora striata, or striated bodies, the thalami nervorum opticorum, or beds of the optic nerves, and the nates and testes. Between the optic beds is a third ventricle, which communicates with a fourth under the cerebellum, the crura of which always form a transverse prominence under the medulla oblongata, called the pons Varolii, or bridge ofVarolius. The eye, invariably lodged in its orbit, is protected by two lids and a vestige of a third, and has its crystalline fixed by the ciliary processes-its sclerotic is simply cellular. The ear always contains a cavity called the tympanum, or drum, which communicates with the mouth by the Eustachian tube; the cavity itself is closed externally by a membrane called the membrana tympani, and contains a chain of four little hones, named the incus or anvil, malleus or hammer, the os O:biculare or circular bone, and the stapes or stirrup; a vestibule, on the entrance of which rests the stapes, and which communicates with three semicircular canals; and, final1y, a |