FUNCTIONS OF QUADRUPEDS. 15 



return through the veins, its nutritive particles have been 

 discharged, it becomes livid and heavy ; and it is only by 

 repassing the heart and lungs that it can regain its former 

 state. The lungs of all the mammiferous animals, as in 

 the human subject, are divided into lobes, lobules, and mi- 

 nute cells, upon which the small branches of the pulmonary 

 arteries are spread. Each of the cells has a tube; and all 

 the tubes of each lobe communicate with one another in the 

 bronchice, and at last terminate in the trachea, or wind- 

 pipe. Both the windpipe and the bronchia? are kept, in 

 an expanded state by elastic cartilaginous rings; so that 

 when the chest is dilated, the external air is enabled, by its 

 own weight, to force itself into all the cells of the lungs. 

 The air is driven out by the contraction of the chest. 



Besides their use in respiration, the lungs of the mammi- 

 ferous animals are also necessary for the production of sound. 

 The upper part of the windpipe is denominated the larynx; 

 and in the centre of this is situated the glottis, which, with 

 its adjacent parts, forms the principal organ of the 'voice. 

 The glottis is capable both of extension and contraction; 

 and when the air, in expiration, is forced from the lungs, 

 and pressed so quickly into the mouth through the contracted 

 glottis, that its. fibres are made to vibrate and communicate 

 their vibrations to the larynx, sounds are produced. The 

 greater or less shrillness of these depends upon the larynx 

 being drawn more or less forward. The sounds are after- 

 wards modulated by the cavity of the mouth and the pecu- 

 liar motions of the tongue. At the larynx of all the quadru- 

 peds there is a cartilage called the epiglottis, which is 

 pressed down by the food, in its way to the gullet, and thus 

 prevents it from entering the windpipe to obstruct the 

 breath. No animals, except those which have true or 

 cellular lungs, can be said to have any voice. The inferior 

 tribes, although they have no true voice, are not, however, 



deprived 



