MAMMALIA. 29 



Between the occipital, the parietal, and the sphenoid, are inserted the tem- 

 poral bones, which, to a certain extent, belong to the face. 



In the foetus the occiput is divided into four parts, the body of the 

 sphenoid into two, and three of its pairs of alse are separate ; tlie temporal 

 bone into tliree, of which one serves to complete the cranium, another to 

 enclose the labyrinth of the ear, the tliird to form the walls of its cavity, &c. 

 These portions of the cranium unite more or less quickly, according to the 

 species, and end by perfect union in the adult. 



The face is formed by the two maxillary bones, between Avhich the 

 nasal canal passes. Before these, are two intermaxillary, behind two palate 

 bones, and between them descends the single plate of the ethmoid bone, 

 named the vomer. At the entrance of the nasal canal are the bones which 

 form the nose. The molar or cheek bone of each side, unites the maxillary to 

 the temporal, and often to the frontal bone ; and finally, the lachrymal cavity 

 occupies the internal angle of the orbit, and sometimes part of the cheek. 



The tongue, in the Mammalia, is always fleshy, and attached to the hyoid 

 bone, which bone is suspended by ligaments to the cranium. 



Their lungs, two in number, are composed of a mass of small cells, 

 inclosed without adhesion in a cavity formed by the sides of the diaphragm, 

 and lined by the pleura. Their organ of voice is at the upper extremity 

 of the trachea or windpipe ; and a fleshy continuation, named velum palati, 

 establishes a direct communication between their larynx and the back part 

 of their nostrils. 



Living on the earth's surface, as do the greater part of the Mammalia, 

 they are exposed to alternations of heat and cold, and their bodies have, in 

 consequence, a covering of hair, which is thicker in the colder, and more 

 scanty in the warmer regions. The Cetacea, which inhabit the sea, are, 

 however, totally destitute of this covering. 



The intestinal canal of the mammiferous animals, is suspended by a fold 

 of the peritonaeum, called the mesentery, Avhich contains numerous con- 

 globate glands for the lacteal vessels. Another production of the perito- 

 nsBum, named the epiploon, hangs before and beneath the intestines. 



The generation of the Mammalia is essentially viviparous. The foetus, 

 after conception, descends into the uterus, to the inner surface of which it 

 is attached by means of an arrangement of vessels, termed the placenta, 

 through the medium of which, nourishment is derived. The young, for 

 some time after birth, are nourished by a particular secretion of the mother, 

 (milk,) produced in the mammiferous animals, after parturition, and dra^vn 

 by the young from mantmcR, or teats. It is from this last character that the 

 term Mammalia has been applied to this class — a character exclusively 

 proper to them, and by which they are more easily recognized than by any 

 other external distinction. The essential characters of the Mammalia are 

 taken from the organs of touch, and the organs of mastication. On the 

 first, depend the power and dexterity of the animal ; and from the second, 



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