236 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



plexity in the higher forms. The secretion of these glands aids in 

 moistening the food, and not infrequently it is adhesive and is used in 

 capturing the prey. In the mammals true salivary glands appear. 

 The saliva secreted by them contains not only mucus, but also a 

 digestive ferment (ptyalin) which changes starch into sugar. The 

 names of the various oral glands (labial, buccal, lingual, retroUngual, 

 etc.) are roughly indicative of their position. 



In the terrestrial amphibia, snakes (fig. 240) and lizards, there 

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

 lary or intemasal gland in the septum 

 between the nasal cavities, as well as 

 palatal glands near the choanae (the inter- 

 nasal gland is lacking in the csecilians). 

 Many reptiles also have a sublingual gland 

 on either side (fig. 250). In many snakes 

 a pair of the labial glands are greatly de- 



chP-ii--.-^{ ''.'"'.Alp 



I /VMWwJVviViAAA, \ 



Fig. 250. — Transverse section of tongue and 

 lower jaw of Lacerta, after Gegenbaur. d, tooth; 

 h, hyoid cartilage; /, labial glands; m, muscles; si, 

 sublingual gland; t, tongue. 



Fig. 251. — Palatal surface of 

 hen, after Heidrich. ch, ante- 

 rior end of choana; gs, openings 

 of sphenopterygoid glands; Ip, 

 m, openings of lateral and 

 medial palatine glands; »n, 

 opening of gl. maxillaris mon- 

 ostomatica. 



veloped and have migrated into the zygomatic liagment, where they 

 have become modified into the well-known poison glands (fig. 240), 

 the ducts of which connect with the poison fangs (p. 228). In the 

 only known poisonous lizard {Heloderma) the sublingual glands furnish 

 the poison. Oral glands are poorly developed in the sea turtles and 

 the crocodilians. 



Birds lack the labial and intemasal glands, but they have numer- 

 ous other glands opening separately into the roof of the mouth (fig. 

 251) as well as anterior and posterior subHnguals and frequently an 



