296 VERTEBRATE ZOOLOGY 



The mouth cavity itself is made up of two regions : the vesti- 

 bule, which is the part between the lips and cheeks and the jaws 

 and teeth, and the mouth proper, or the part between the teeth 

 and the soft palate. 



The roof of the mouth is formed by the hard and the soft palate. 

 The hard palate, which is the anterior portion, is characterized by 

 a number of transverse ridges and is backed by the premaxillary, 

 maxillary, and palatine bones. At the anterior end of the hard 

 palate and immediately behind the incisor teeth, is a pair of 

 obscure openings which lead into the organs of Jacobson, a pair 

 of small sensory organs of uncertain function which lie in the floor 

 of the nasal cavity. 



The soft palate is the soft flap which forms the hinder portion 

 of the roof of the mouth. The narrow space forming the hinder 

 part of the mouth cavity, bounded dorsally by the soft palate and 

 by the root of the tongue ventrally, is called the isthmus faucium ; 

 on each side of it lies the prominent tonsil. 



The floor of the mouth is formed mainly by the tongue, which is 

 a muscular organ projecting from it. The free end of the tongue 

 is joined with the floor of the mouth by means of a median fold 

 called the frenulum. The upper surface of the tongue is provided 

 with three kinds of taste papillae, the fungiform, circumvallate, 

 and foliate. The fungiform papillae are minute projections cover- 

 ing the anterior portion of the tongue ; the circumvallate papillae 

 are a pair of prominent elevations near its hinder end, rising each 

 from a depression; the foliate papillae are a group of parallel, 

 transverse ridges lateral and anterior to each circumvallate papilla 

 and opposite the last pair of molar teeth. 



The pharynx lies just back of the soft palate. Two passages 

 open into it at its anterior end and two at its posterior end. The 

 two anterior passages are the isthmus faucium (the hinder end of 

 the mouth cavity) and the nasopharynx. This latter space is a 

 part of the respiratory passage ; it lies immediately above the soft 

 palate and the hinder part of the hard palate, and communicates an- 

 teriorly with the nasal cavities and posteriorly with the pharynx. 

 Exercise 22. Draw a diagrammatic sketch showing the cavity of the 

 mouth and the pharynx. 



