220 



COMPARATIVE MORPHOLOGY OF VERTEBRATES. 



The dorsal surface is usually covered with a soft epithelium, developed 

 into papillae of varying shapes, some being sensory in character, and 

 some are occasionally (monotremes, felidae) cornified. 



The skeleton of the mammalian tongue (hyoid apparatus) varies 

 considerably. In its most complete development it consists of a body 

 (copula of the hyoid and first branchial) in the median line, which bears 

 two pairs of cornua. The anterior pair (lesser horns of human 

 anatomy) are usually elongate, and consist of a series of ossicles (p. 101) 

 connecting the body with the otic region of the skull. The second 

 pair (greater cornua of man) are occasionally absent. In man the 

 greater part of the anterior cornua is represented by the stylohyoid 

 ligament, the proximal portion being fused to the skull as the styloid 

 process. 



Oral Glands. 



In the cyclostomes there is a large, so-called 'salivary gland' of 

 unknown function, opening into the mouth on either side below the 

 tongue. With this exception, glands are lacking from the mouths of 

 aquatic ichthyopsida. With the assumption of pulmonate respiration 

 and more terrestrial habits, the mouth is no longer constantly bathed 



with water and so glands appear, 

 increasing in number and com- 

 plexity in the higher forms. The 

 secretion of these glands aids in 

 moistening the food, and not in- 

 frequently it is adhesive and is 

 used in capturing the prey. In the 

 mammals true salivary glands ap- 

 pear. The saliva secreted by them 

 contains not only mucus, but also a 



FIG. 224 .-Transverse section of tongue digestiye f er ment (ptyalin) which 



.and lower jaw of Lacerta, after Gegenbaur. 



d, tooth ;h, hyoid cartilage;/, labial glands; changes Starch into SUgar. 



m, muscles; si, sub lingual gland; t, tongue. 



The 



names of the various oral glands 

 (labial, buccal, lingual, retrolingual, etc.) are roughly indicative of 

 their position. 



In the terrestrial amphibia, snakes (fig. 215) and lizards there are 

 labial glands, opening at the bases of the teeth, and an intermaxil- 

 lary or internasal gland in the septum between the nasal cavities, as 

 well as palatal glands near the choanae (the internasal gland is lacking 



