THE MOUTH 225 



The salivary secretion contains an amylolytic enzyme, 

 termed ptyalin, which is capable of acting on cooked starchy 

 foods. At birth only the secretion of the parotid gland 

 contains ptyalin, but, although the enzyme appears in the 

 submaxillary and sublingual secretions during the third month, 

 its amylolytic action is not completely developed until the end 

 of the first year. The amylolytic action of the pancreatic 

 secretion is similarly delayed, and hence it follows that but 

 little starchy food should be given to children until they are 

 a year old. 



Calcium salts are present in the saliva, more especially in 

 the secretion of the submaxillary gland. The latter fact 

 accounts for the deposition of tartar on the mandibular teeth 

 and for the occurrence of submaxillary calculi. 



The nervous mechanism of the salivary secretion is referred 

 to on page 189. 



The Mouth. The mucous membrane of the cheeks, gums, 

 lips and floor of the mouth is entirely supplied by the trigeminal 

 nerve. Reference has already been made to the results of anaes- 

 thesia of the cheeks and lips (p. 75) and to the similar results 

 of paralysis of the buccinator (p. 84), which constitutes the 

 chief muscular stratum of the cheek. 



The mucous membrane of the gums is firmly adherent to the 

 periosteum, and consequently the accumulation of pus under 

 the mucous membrane is associated with severe local pain. 



The lymph vessels of the gums do not all follow the same 

 course. Those from the inner surface of the maxillary gums 

 pass to the ureter and anterior group of the deep cervical 

 lymph glands (p. 222), while those from their outer surface 

 terminate in the submaxillary lymph glands (p. 221). The 

 lymph vessels from the anterior part of the outer surface of the 

 mandibular gums follow the lymph vessels from the central 

 part of the lower lip and end in the submental lymph glands, 

 which lie on the mylo-hyoid muscles, immediately below the 

 chin ; all the remaining lymph vessels from the mandibular 

 gums join the submaxillary group. 

 '5 



