THE DIGESTIVE SYSTEM 71 



Papillae cover the dorsal surface of the anterior three- 

 quarters of the tongue, the tip, and dorsal portions of the 

 lateral surfaces. They are entirely lacking on the pos- 

 terior quarter of the upper surface, ventral portions of 

 the lateral surfaces, and the under side of the free an- 

 terior end. The filiform papillae are slender pointed struc- 

 tures with their tips generally directed backward. On the 

 anterior half of the dorsal surface these papillae are rather 

 conspicuous when seen under the dissecting microscope. 

 In a triangular area about half way between the anterior 

 and posterior ends of the tongue the filiform papillae are 

 larger than elsewhere, conical and erect. The filiform 

 papillae back of this area are so numerous and slender that 

 here the tongue has a velvety appearance under the dis- 

 secting microscope. A few, low, cylindrical fungiform 

 papillae are scattered over the anterior half of the dorsal 

 surface, chiefly toward the tip. 



There is no organized tonsil. This organ is represented 

 merely by scattered follicular openings on the longitudi- 

 nally folded side walls of the narrow faucial canal. 



Exercise XX. Sketch a dorsal view of the tongue. 



The soft palate forms the ventral floor of the naso- 

 pharynx (pars nasalis). This is a relatively large cavity 

 which opens anteriorly through the single posterior naris 

 into the nasal cavity. Toward its posterior end the naso- 

 pharynx curves downward and opens into the pharynx 

 proper. The lateral walls are supported by the sphenoid 

 processes of the palatine bone and the median pterygoid 

 processes of the alisphenoid, while the basisphenoid and 

 presphenoid bones support the roX)f. The auditory (Eus- 

 tachian) tubes from the middle ears open into the naso- 

 pharynx about half a centimeter from the posterior border 

 of the soft palate. The opening of each tube is a longi- 

 tudinal slit near the angle between the lateral and dorsal 



