DIGESTIVE ORGANS. 



221 



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, 

 though absent from the cetacea, form a distin- f ace O f hen, after Heid- 

 guishing feature of the group. These salivary rich - ch > anterior end of 



. . J choana; gs, openings of 



glands are usually in the neighborhood of the sphenopterygoid glands; 

 mouth, but one or more of them may be carried j; ^ p ^T^ 

 back into the neck (fig. 226), but in all cases the eral and medial palatine 



, , . , . , glands; m, opening of 



homologies are decided by the openings of the g i. maxiiiaris monosto- 

 ducts. The salivary glands include the sub- matica - 

 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. 



