DIGESTIVE ORGANS. 



221 



chl 



--\Y/n 



'VP 



in the caecilians). Many reptiles also have a sublingual gland on either 



side (fig. 224). In many snakes a pair of the labial glands are greatly 



developed and have migrated into the zygomatic ligament, where they 



have become modified into the well-known poison glands (fig. 215), 



the ducts of which connect with the poison fangs 



(p. 213). In the only known poisonous lizards 



(Heloderma) the sublingual glands furnish the 



poison. Oral glands are poorly developed in 



the sea turtles and the crocodilians. 



' Birds lack the labial and internasal glands, 



but they have numerous other glands opening 



separately into the roof of the mouth (fig. 225) 



as well as anterior and posterior sublinguals and 



frequently an 'angle gland' at the angle of the 



mouth, which may be the last remnant of the 



labial glands of the other Sauropsida. 



Besides numerous smaller glands (labials, 

 buccals, linguals, palatines) imbedded in the 

 mucous membrane and opening separately into 

 the mammalian mouth, the salivary glands, 



, , . ' . .. . FIG. 225. Palatal sur- 



though absent from the cetacea, form a distm- face O f hen, after Heid- 

 guishing feature of the group. These salivary ri u ch - ^, anterior end of 



' choana; gs, openings of 



glands are usually in the neighborhood of the sphenopterygoid glands; 

 mouth, but one or more of them may be carried 

 back into the neck (fig. 226), but in all cases the 

 homologies are decided by the openings of the 

 ducts. The salivary glands include the sub- 

 maxillary and sublingual of the lower groups, and in addition the 

 parotid gland, apparently a development within the class. The sub- 

 maxillary normally lies in the lower jaw beneath the mylohyoid 

 muscle, and its duct (Wharton's duct) opens near the lower incisor 

 teeth. Near this is frequently a retrolingual gland, its duct open- 

 ing near the former. The sublingual gland occurs between the tongue 

 and the alveolar margin of the lower jaw and usually empties by 

 numerous duct. The parotid gland has its normal position near the 

 ear and its ducts (Stenon's duct) pours the secretion out near the 

 molars of the upper jaw. Other oral glands are occasionally present, 

 like the molar glands of ungulates and the orbital glands of dogs, 

 both of which have ducts leading into the mouth. 



eral and medial palatine 



glands; m, opening of 



g i. maxiilaris monosto- 

 matica - 



