THE BUCCAL CAVITY. 15 



b. Paired apertures. 



i. The Nostrils or anterior nares are two small open- 

 ings on the dorsal surface of the head, close to its 

 anterior end. 



B. The Buccal Cavity. 



Open the mouth to its full extent : note the wide buccal or mouth 

 cavity, of ivhich the hinder 'part or pharynx is continued hack into 

 the (esophagus. Note also the following structures : 



1. On the Roof of the Mouth. 

 a. The Teeth. 



i. The maxillary teeth are a row of fine teeth, 



attached round the edge of the upper jaw. 

 ii. The vomerine teeth are two small patches of sharp 

 teeth in the fore part of the roof of the mouth 

 and near the middle line. 

 h. The posterior nares are two small holes Ij^ing to the outer 

 sides of and slightly in front of the two patches of 

 vomerine teeth. 



Pass bristles through the nostrils, and see that they 

 come out through the posterior nares into the buccal cavity. 



c. The Eustachian tuhes or recesses are a pair of much 



larger holes, at the sides of the posterior part of the 

 buccal cavity. Each hole opens into a slightly dilated 

 chamber — the tympanic cavity — which is closed 

 externally by the tympanic membrane already seen 

 on the surface of the head. 



Perforate the tympanic membrane on one side ivith a 

 needle, and pass a bristle or seeker through the hole and 

 down the Eustachian tube into the mouth. 



d. Two rounded jjrominences at the sides of the roof of 



the mouth are caused by the eyeballs. 



Press down one of the eyes with your finger, and note 

 that it can be made to project very considerably into the 

 buccal cavity. 



% On the Floor of the Mouth. 



a. The lower jaw, which is devoid of teeth, forms a bony 

 margin to the floor of the mouth : the rest of the floor 

 is soft and fleshy, but is slightly stiffened by a car- 

 tilaginous plate — the body of the hyoid. 



