534: THE TRACHEA. 



trie nerve, a most extensive organic connection, as already 

 shown, is maintained between the organ of voice and the 

 functions of digestion, respiration and circulation, through 

 the agency of the laryngeal, pharyngeal, cardiac, pulmo- 

 nary, cesophageal, and gastric branches of this pneumo- 

 gastric nerve, associated with the great sympathetic of the 

 neck, chest, and abdomen. But the most important rela- 

 tion of the larynx to the dentist is that which it has with 

 the mouth. 



Here the anatomical and physiological relationship is 

 most close and important. The same mucous membrane 

 extends from the one cavity into the other from the 

 mouth into the larynx. Blood-vessels and nerves, from 

 the same sources also associate the two sets of organs, and 

 lesion or destruction of the one, not only cripples and de- 

 stroys its own functions, but also extends in greater or less 

 degree to those of the other. For example, the loss of 

 teeth, a cleft palate, swollen tonsils, hare-lip, &c., illus- 

 trate the injury inflicted upon the voice as well as the 

 speech, in the subversion of the natural relations of the 

 mouth and larynx, by this structural change in the organs 

 belonging to the mouth. 



The same result would follow should the larynx be 

 altered from its natural condition by change in any of its 

 parts. 



Trachea (Vpa^ss rough.) The trachea (or arteria as- 

 pera) is situated upon the median line of the neck, between 

 the larynx above, to which it is connected, and the bron- 

 chia below into which it divides. It commences about the 

 fifth cervical vertebra below the larynx, and descends in 

 front of the oesophagus and vertebral column, into the 

 chest, behind the arch of the aorta, and in front of the third 

 dorsal vertebra, where it terminates, dividing into the right 

 and left bronchi, which go to the lungs. Its length and 

 diameter vary according to age and sex, but the average in 

 the adult is about five inches in length, and from three- 

 quarters to one inch in diameter. 



The structure of the trachea consists of cartilage, fibrous 



