42 



ANATOMY. 



nects in front with the outside air through the nostril and be- 

 hind with the pharynx through an opening which may be called the 

 posterior nostril or technically, the posterior nares. Each cham- 

 ber also connects laterally with the sinuses of the head (shown 

 in class). The floor, roof and sides are formed by the various 

 face bones together with portions of the frontal, ethmoid, and 

 sphenoid, and the median cartilage already mentioned. 



Pharynx. — This is a muscular sac situated beneath the 

 cranium, and back of the soft palate which constitutes a partition 

 between the pharynx and mouth cavities. This organ belongs 

 to both the respiratory and digestive systems. Its walls are com- 

 posed of two coats : the inner mucous and outer muscular. It 

 connects by openings with the nasal chambers above, with the 

 mouth in front, and with the oesophagus behind, with the lungs 

 below, and on each side with the Eustachian tube to the middle 

 ear. 



i/VATER 



OXYGEN 



HEAT 



CARBON -Dl- OX/Dt 



LUNGS 



BLOOD 



GA5 



BODY T/SSUfS 



FIG. 21. RESPIRATION IN DIAGRAM. (M. H. R.) 



Larynx. — A cartilaginous box located at the upper end of the 

 trachea and composed of five pieces — one epiglotis. one thyroifl. 

 two arytenoids, one cricoid. Twelve muscles attach to these car- 

 tilages for the purpose of controlling them. 



The epiglotis (a sort of lid) is a tongue-shaped piece of 

 flexible cartilage which covers the entrance to the larvnx. It 

 is held down against the arytenoid cartilages when food is swal- 

 lowed, but immediately afterward moves upward and thus opens 

 the entrance to the larynx. It remains in this position during 

 respiration. 



