532 VERTEBRATE LIFE AND ORGANIZATION 



Epiglottis 



-Vocal cordS' 

 Glottis- 

 "Laxynizal cartilages ' 



A B 



Figure 26.8. A laryngoscopic view of the vocal cords, looking into the larynx 

 from above. A, normal position of vocal cords; B, position of cords during speech. 



minute foreign particles are entrapped in a sheet of mucus, wliich is 

 carried by ciliary action into the pharynx where it is swallowed or 

 expectorated. Inspired air is moistened in primitive tetrapods such 

 as the frog, but cold-blooded tetrapods in general do not need as much 

 conditioning of the air as birds and mammals. 



Air continues through the internal nares, passes through the 

 pharynx, and enters the larynx, which is open except when food is 

 swallowed. The raising of the larynx during swallowing can be demon- 

 strated by placing your hand on the Adam's apple, the external 

 protrusion of the larynx. The epiglotrls Hips back over the entrance 

 of the larynx when it is raised. 



The larynx is composed of cartilages derived from certain of the 

 visceral arches, and serves both to guard the entrance to the windpipe, 

 or trachea, and to house the vocal cords (Fig. 26.8). The vocal cords 

 are a pair of folds in the lateral walls of the larynx. They can be 

 brought close together, or be moved apart, by the pivoting of laryngeal 

 cartilages connected to their dorsal ends. When we speak, they are 

 moved toward each other and the current of air expelled from the 

 lungs sets them vibrating. They in turn vibrate the column of air in 

 the larynx, pharynx and mouth, just as the reed in an organ pipe 

 vibrates the column of air in the pipe. Muscle fibers extending between 

 the various cartilages of the larynx control the tension of the cords 

 and the pitch of the sound. The shape of the pharynx, mouth, tongue 

 and lips affects the final quality of the sound. The glottis is the opening 

 into the larynx between the vocal cords. 



The trachea extends down the neck and finally divides into 

 bronchi that lead to the pair of lungs. Unlike the esophagus, which 

 is collapsed except when a ball of food is passing through, the trachea is 

 held open by C-shaped cartilaginous rings and air can move freely back 

 and forth. Its mucosa continues to condition the air. 



The lungs of amphibians lie in the anterodorsal part of the pleuro- 

 peritoneal cavity, which is the larger part of the coelom. (The peri- 

 cardial cavity is the other part.) In most higher vertebrates, the pleuro- 

 peritoneal cavity is subdivided into a pleural cavity around each lung 

 and a peritoneal cavity housing the abdominal viscera. The pleural 

 cavities of mammals lie within the chest, or thorax, and are separated 

 from the peritoneal cavity by a muscular diaphragm. A coelomic 

 epithelium, the pleura, lines the pleural cavities and covers the lungs. 

 Each bronchus enters a lung, accompanied by blood vessels and nerves, 

 in a mesentery-like fold of pleura (Fig. 26.7). 



