198 DIGESTION MASTICATION, INSALIVATION, DEGLUTITION. 



surface of the soft palate are larger and here form a continuous layer. The 

 glands of the tongue are situated beneath the mucous membrane, mainly on 

 the posterior third of the dorsum ; but a few are found at the edges and the 

 tip, and there is a gland of considerable size on either side of the frenum, 

 near the tip. All of these are small, racemose glands, similar in structure to 

 those which have been called the true salivary glands. In addition to these 

 structures, the mucous membrane of the tongue is provided with simple and 

 compound follicular glands, which extend over its entire surface, but are 

 most abundant at the posterior portion, behind the circumvallate papillae. 

 The most important of the glands of the tongue will be described in connec- 

 tion with the physiology of gustation. 



In the pharynx and the posterior portion of the buccal cavity, are the 

 pharyngeal glands and the tonsils. In the pharynx, particularly the upper 

 portion, racemose glands, like those found in the mouth, exist in large num- 

 bers. The mucous membrane .is provided, also, with simple and compound 

 mucous follicles. The tonsils, situated on either side of the fauces between 

 the pillars of the soft palate, consist of an aggregation of compound follicular 

 glands. The number of glands entering into the composition of each tonsil 

 is ten to twenty. 



The secretion from the glands and follicles above enumerated can not be 

 obtained, in the human subject, unmixed with the fluids from the true sali- 

 vary glands. It has been collected in small quantity, however, from the in- 

 ferior animals, after ligature of all the salivary ducts. This secretion is simply 

 a grayish, viscid mucus, containing a number of leucocytes and desquamated 

 epithelial scales. It is this which gives the turbid and opaline character to 

 the mixed saliva, as the secretions of the salivary glands are all perfectly 

 transparent. The fluid from these glands in the mouth is mixed with the 

 salivary secretions ; and that from the posterior part of the tongue, the ton- 

 sils, and the pharyngeal glands passes down to the stomach with the aliment- 

 ary bolus. This secretion, consequently, forms a constant and essential part 

 of the mixed saliva. 



Mixed Saliva. Although the study of the distinct secretions discharged 

 into the mouth possesses considerable physiological importance, it is only the 

 fluid resulting from a union of them all, which can properly be considered in 

 connection with the general process of insalivation. In man it is necessary 

 that the cavity of the mouth should be continually moistened, if for nothing 

 else, to keep the parts in a proper condition for phonation. A little reflec- 

 tion will make it apparent that the flow, from some of the glands at least, is 

 constant, and that from time to time a certain quantity of saliva is swallowed. 

 The discharge of the fluid into the mouth, though diminished, is not arrested 

 during sleep. In the review of the different kinds of saliva, it has been seen 

 that the flow from none of the glands is absolutely intermittent ; unless it be so 

 occasionally from the parotid, the secreting action of which is most powerfully 

 influenced by the act of mastication and the impression of sapid substances. 



Upon the introduction of food the quantity of saliva is greatly increased ; 

 and the influence of the sight, odor, and occasionally even the thought of 



