METABOLISM IN VERTEBRATES 



Fig. 3.9. Trachea, bronchi, and air passages of the lung in a mammal. (Photo- 

 graph of plastic cast of the air passages of the lungs courtesy Ward's Natural 

 Science Establishment.) 



laminated outgrowths found along the sides of the pharyngeal pouches in 

 fishes and some amphibians (see Fig. 5.31, p. 169). They are covered by a 

 very thin layer of cells beneath which is a rich capillary bed. Lungs lie 

 deep in the body and are connected to the pharynx by air passages; the lungs 

 and air passages comprise the respiratory system. 



The opening from the pharynx into the larynx, an expanded portion of the 

 air passages containing the vocal cords, is known as the glottis. A tube called 

 the trachea passes, alongside the esophagus, from the larynx into the chest, 

 or thorax. There, the trachea divides into two bronchi which enter the lungs. 



55 



