THE DIGESTIVE SYSTEM 



303 



the duct of which opens between the intermaxillary bones. In some 

 amphibia, e.g., Rana, mucus glands are also located in the posterior 

 narial passages. That enzymes are secreted by the mucus cells of fishes 

 and amphibia has, however, not been demonstrated. 



In the reptiles, there are serous cells in the oral glands, and lingual, 

 sublingual, and palatine glands occur. Glands connected with the teeth 

 are dififerentiated as the poison glands of some snakes. 



True salivary glands secreting enzymes are limited to mammals. 



There seems no good reason to doubt, however, that the salivary 

 glands of mammals are derived from the oral glands of reptiles. Labial 

 and buccal glands become abundant, and possibly the parotid is an 



.COMPOUND 

 TUBULAR GLANO 



. /emus OR 



Fig. 254. — Various types of digestive and endocrinal glands which develop from the 

 endodermal (mucous) lining of the alimentary canal. The endocrine glands are ductless. 

 The digestive glands may be simple or compound, tubular or alveolar (acinous). 

 (Redrawn after Braus.) 



enlarged buccal gland. In addition to the lingual and palatine glands, 

 the sublingual and submaxillary glands are present; and in general, the 

 glands of man resemble those of other primates. 



The Tongue 



The tongue is a muscular organ of miscellaneous functions — digestive, 

 sensory, conversational — lying in the floor of the mouth cavity and 

 attached to the hyoid bone. It consists of an apex or body directed 

 towards the teeth of the lower jaw, a root of muscular attachment, a 

 dorsum divided by the sulcus terminalis into an anterior papillated por- 

 tion and a posterior tonsillar and glandular portion, and an inferior surface 

 below the apex. The sulcus terminalis is a V-shaped groove with the 

 apex of the V pointing backwards and marking the position of the foramen 

 coecum. Fig. 255. 



The dorsum of the tongue anterior to the sulcus is covered with 

 numerous papillae which give the tongue its characteristic rough appear- 

 ance. Four kinds of papillae are distinguished, vallate, filiform, foliate, 

 and fungiform. . The vallate papillae are the largest, and are distinguished 

 also by the deep depression or fossa which surrounds each of them. On 



