NUTRITION 



369 



secretion. These cells are developed on the inner walls of a cavity 

 which usually opens into some other organ by way of a tube called 

 a duct. 



These cavities may be simple and very small, like the mucous 

 glands that moisten all the digestive tract, or they may be very 

 large and complex like the liver. In either case they must have a 

 rich blood supply and nerves to control it and the action of the 



TEMPORARY SET. > 

 PERMANENT SET 



CHART S H O W INfr ORDER 



SUCCESSION AMD Tine OF rut 



CE OF TEETH 



FIG. 117. 



gland, as well. A gland, then, consists of the secreting cells, the 

 gland cavity, the ducts, the blood and nerve supply. 



Salivary Glands. The principal glands of the mouth are the 

 salivary glands of which there are three pairs. The largest pair is 

 located beneath the ear on each side of the head and the ducts open 

 opposite the second upper molar. Inflammation of the glands 

 causes the mumps. The sub-maxillary glands lie within the angles 

 of the lower jaw and the sub-lingual pair are below the tongue, 

 beneath the floor of the mouth; ducts from both pairs open under 

 the middle of the tongue. 



