Chap. 13 THE RELEASF. OF ENERGY RESPIRATION 241 



birds, a kind of historical larynx is present in the typical position, but without 

 vocal cords. Another and different kind of voice box, the syrinx, is located at 

 the junction of the bronchi. The whole bird chorus depends upon the syrinx, 

 such a range of sounds as those of parrots and thrushes, crows and robins. 



Characteristic features of the mammalian larynx are its cartilaginous cover, 

 the epiglottis, which is quickly pulled down in swallowing, and the strongly 

 developed vocal cords (Fig. 13.14). The framework of the larynx is a group 

 of cartilages held together by muscle; the odd-shaped thyroid cartilage that 

 protrudes from the front of the neck is especially large in human males, and 

 known as Adam's apple. The contractions of muscles between the cartilages 

 change the shape of the larynx and vary the size of the opening between the 

 vocal cords. The pitch of the voice is determined by the length of the cords; 

 low with longer cords and high with shorter ones. Pitch can be modified 

 voluntarily. By persistent effort, a voice can be pulled away from the front 

 teeth where it sounds like an alarm clock, and placed properly in the larynx 

 where its tones may become clear and mellow. 



Special Ways of Breathing 



Coughing is a quick inspiration followed by contraction of abdominal 

 muscles, causing an increase of pressure in the thorax. The throat contracts 

 and the glottis is closed. After a certain amount of pressure gathers in the 

 lungs, the air escapes with a rush, pushing open the glottis and carrying with it 

 crumbs or other extraneous material. Coughing is generally a reflex act result- 

 ing from stimuli in the mouth and throat. Psychic coughing is stimulated by 

 hearing someone else cough. 



A sneeze is a violent expiration with the air thrown into the nose and 

 against the hard palate. 



Hiccoughs (hiccups) are due to the spasmodic contraction of the diaphragm 

 and a sudden inspiration cut short by the snaplike closure of the glottis. They 

 are often stimulated by very hot fluid taken into an empty stomach. 



Sighing is a prolonged inspiration followed by a deep expiration, often with 

 fading voice. 



Yawning is similar to sighing but is accompanied by stretching of the lower 

 jaw, sometimes of legs and arms. 



Snoring is an accompaniment to deep breathing through the mouth. The 

 treble is the vibration of the soft palate. 



Dyspnea is labored breathing due to choking, reduced absorptive surface of 

 lungs as in pneumonia, or lack of oxygen in the air. 



Purring is probably caused by vibration of air drawn across the false vocal 

 cords by a comfortable cat, a social expression that corresponds in satisfaction 

 to human humming. 



