236 VERTEBRATE ZOOLOGY 



angular cartilage directly in front of the glottis, which prevents 

 food from entering it when passing through the pharynx. 



Exercise 27. Draw a diagrammatic sketch showing the cavity of the 

 mouth and pharynx. 



The Respiratory System. This system consists of the nasal cav- 

 ities, the nasopharynx, the pharynx, the trachea with the larynx, 

 the bronchi, and the lungs. 



The nasal cavities are two in number, and lie side by side in 

 the anterior portion of the head, separated by a median partition, 

 the nasal septum. They communicate with the outside through the 

 nostrils, or external nares, and with the nasopharynx through the 

 internal nares. Cut away the soft palate and the hinder part of 

 the hard palate and expose the nasopharynx and the posterior 

 nares. Note a pair of slits in the lateral walls near the middle of 

 the nasopharynx : these are the openings of the Eustachian tubes, 

 which join the middle ear with the pharynx. 



The nasal cavities are rendered very irregular in outline and 

 are almost entirely filled by projections from their walls. These 

 projections are called the turbinals and serve to increase the sen- 

 sory surface ; they will be studied with the skeletal system. 



Make a transverse section of the anterior end of the nose, using 

 a large scalpel. The cartilaginous nasal septum will be seen be- 

 tween the two nostrils. From its dorsal edge on each side a thin 

 plate passes laterally, then ventrally, and finally dorsally, forming 

 the sides of the cavity. 



Exercise 28. Draw the transverse section. 



Observe the trachea and the larynx, and the organs lying near 

 them. Just dorsal to the trachea is the oesophagus, a long, mus- 

 cular tube, which extends from the pharynx to the stomach. On 

 each side of the trachea are the carotid artery and the internal 

 jugular vein, and also a nerve cord composed of the vagus and 

 sympathetic nerves closely bound together ; these nerves must not 

 be cut. Near the anterior end of the trachea is the thyroid gland. 



Dissect from the body the tongue with its long, supporting hyoid 

 bones, the larynx and trachea, and the lungs, and put them 



