438 ELEMENTA RY ANA TOM Y. [LESS. 



exist in the tongue and in the inside of the skin investing 

 the jaws, as in many Reptiles, these latter structures 

 answering to our buccal glands, as do also the salivary glands 

 of harmless Serpents. Poisonous Serpents however are pro- 

 vided with an extra glandular structure, placed beneath and 

 behind the orbit. This gland it is which secretes the venom, 

 and its ducts convey the poisonous fluid to the base of 

 the deeply-grooved poison fang described in the Seventh 

 Lesson. By a very rare and remarkable exception, the 

 poison gland may (as in Callophis intestinalis) attain enor- 

 mous proportions, extending backwards as far as the heart, 

 being lodged in the general cavity of the body. 



In the class of Birds we may find sub-maxillary glands 

 occupying the whole of the anterior part of the space included 

 by the rami of the lower jaw ; or, as in the Woodpecker, a 

 single gland extending from between the angles of the man- 

 dible to its symphysis, and furnished with a distinct duct. 



In man's own class, both the number and relative size of 

 the silivary glands may differ from what we find in him. 

 Thus there may be, as in the Dog, an extra structure, called 

 the zygomatic gland, placed in the floor of the orbit, behind 

 the anterior root of the zygoma (its duct opening opposite 

 the last true molar), and also another, the second, or accessory 

 sub-in:ixillary gland, smaller, and placed beneath the true 

 sub-maxillary, its long duct opening close to the aperture of 

 the true sub-maxillary of the same side. 



The parotid also, as in the same animal, may be some- 

 what smaller in size than the sub-maxillary, but this dispro- 

 portion is insignificant in comparison with that produced by 

 the enormous development which the sub-maxillary glands 

 sometimes acquire, as in the Ant-eaters, where these glands 

 meet together and unite on the chest, superficially to the 

 sternum. The sub-maxillary ducts may each be connected 

 with a dilated vesicle, or salivary bladder, as in the Arma- 

 dillos ; or they may branch out and break up, opening by 

 many minute orifices on the floor of the mouth, as in the 

 Echidna ; or each may remain single, but take a very tortuous 

 course, as in the Ornithorhynchus. Parotid glands may be 

 absent (the other salivary glands being present) in man's own 

 class, as in the Monotremes. 



6. Man's TONGUE is a muscular body connected with the 

 os hyoides in the way already noticed in the Eighth Lesson. 

 Its under surface is bound down by a fold of mucous mem- 

 brane, called the fr&num, which proceeds from the middle 



