350 PHILOSOPHY OF ZOOLOGY. 



On the dorsal side of the thyroid cartilage, are two other 

 cartilages, termed ArytenM. To the side of each of these 

 cartilages, and joined to the internal angle of the thyroid, 

 there is attached a broad fibrous band, which forms the mar- 

 gin of the opening into the windpipe or rima glottidis. 



This singular structure of the larynx is not necessary to 

 respiration, but is subservient to the purposes of voice or 

 speech. The air that is expelled from the lungs being 

 acted upon by the variations in the form and tension of 

 the rima glottidis, produces those various sounds by which 

 different species are distinguished. The precise manner in 

 which these sounds are formed, does not appear to be es- 

 tablished. By different authors it has been compared to a 

 drum, a violin, a flute, and an eolian harp. 



Several glandular bodies are connected with the larynx, 

 whose functions have not yet been satisfactorily explained. 

 The largest cf these is the thyroid gland, so called, be- 

 cause it is in part situated on the thyroid cartilage. It 

 consists of two lobes, which descend on each side the wind- 

 pipe. Two glands are likewise seated at the base of the 

 arytenoid cartilages, which appear to secrete the fluid with 

 which the inner surface of the larynx is moistened. Another 

 glandular body at the root of the epiglottis, appears to se- 

 crete a fatty substance. 



In consequence of the liberal supply of serous fluid to 

 the surface of the larynx and windpipe, and, we may add, 

 the cells of the lungs, the air which is returned from the 

 lungs is always found to be loaded with moisture. In man, 

 the quantity given out during twenty-four hours has been 

 rated by some as low as six ounces, and by others as high 

 as twenty. 



In -order to ascertain the changes which the blood under- 

 goes when thus exposed to the influence of the air, it will 



