76 CLASS MAMMALIA. 



The tongue is always fleshy, and is attached to a 

 bone called the hyoid, suspended by ligaments to 

 the cranium. 



Their lungs, two in number, composed of an in- 

 finity of small cells, are always enclosed, without 

 adhesion, in a cavity formed by the ribs and the 

 diaphragm, and lined with the pleura. 



Their organ of voice is always at the superior ex- 

 tremity of the trachea or windpipe ; and a fleshy 

 continuation denominated the velum palati or soft 

 palate establishes a direct communication between 

 the larynx and the back part of the nostrils. 



Living on the earth's surface, these animals are 

 less exposed to the alternations of heat and cold, 

 and consequently their covering, the hair, is of a 

 moderately thick texture, and is not unusually found 

 very slight in the natives of the warmer latitudes. 

 The cetacea, however, which inhabit the water are 

 totally destitute of this covering. 



Their intestinal canal is suspended by a fold of 

 the peritoneum, called the mesentery, which con- 

 tains a number of conglobated glands for the lacteal 

 vessels. Another production of the peritoneum, 

 called the epiploon, hangs in the front of, and un- 

 derneath the intestines. 



The generation of the mammalia is essentially vi- 

 viparous. The foetus, immediately after conception, 

 descends into the matrix; enclosed in its mem- 

 branes, the most external of which, is called the 

 chorion, it attachs itself to the sides of the womb 

 by one or more plexuses of vessels called placentas, 



