The cellular or areolar tissue forms an in tricate network throughout the whole struc ture of the saliyary glands, and can be dis tinctly traced to proceed along the course of the duct and its primary, secondary, and ulti mate subdivisions. It unites together, more or less firmly, the different lobes and lobules, ultimately expanding over the primary aggre gations of the vesicles of the gland, where it is lost to observation, not appearing to extend between each individual vesicle. The spaces, then, between the lobes and lobules are filled up with areolar tissue, which forms a kind of rete for the ramifications of the arteries, veins, and nerves.
The vascular supply.—This is derived from small branches which penetrate the areolar tissue at different points of the surface, and are conducted, as it were, by this tissue through the interlobular spaces as far as the primary aggregations of the vesicles, where they form a network, which is distributed over the elementary parts of the gland, as seen in fig. 306, the vascular arrangement in the parotid of a pig, from a preparation of Mr. Quekett's, and in which the capillary vessels range from the to of an inch.
The nervous supply.— The nerves are de rived partly from the cerebro-spinal, and partly from the sympathetic system, and form a plexus around the arteries, which is ulti mately lost in the interior of the gland. Their exact distribution, however, has not yet been accurately determined.
The arrangement and course of the lym phatics have yet to be made the subject of investigation.
The salivary glands are particularly called into play during mastication; and in order clearly to understand their relative import ance, it will be necessary briefly to consider the nature of that process.
The food having been taken into the mouth, is, in the first instance, coarsely divided by the incisor teeth ; and this divi sion takes place by the alternate elevation and depression of the lower upon the upper jaw. This having been accomplished, the food is next submitted to the action of the molars, reaching the back part of the dentar arches, where the rotatory or grinding movement, brought about by the pterygoid muscles, is peculiarly exerted. Here its ultimate mechanical reduction and intimate admixture with the saliva from the parotid takes place in the following manner :—By the elevation of the jaw and the rotatory move ment of the above muscles, it is akernately passed from between the two sets of teeth to between the latter and the cheeks on the one hand, and the tongue on the other. The
buccinator contracting, urges it again betvveen the two sets of teeth, from which it passes between them and the tongue, and is pushed, by the contraction of the muscles of that organ, again to its original position, between the den tar arches. These different movements are alternately kept up until the entire mass of food has assumed its requisite state of me chanical reduction, and during them the saliva flows down from the orifice of Steno's duct, becoming intimately incorporated with it, and aiding most materially in its integral sub division.
It is worthy of remark, that the position of the terminal portion of Steno's duct, or rather that part of it which passes between the fibres of the buccinator muscle, is such that it must be pressed upon during the contraction of the muscle at that parti cular time when by the same action the food would be placed betv% een the two sets of molar teeth, and the saliva not be immediately required. During the relaxation of the buc cinator, on the contrary, and when the food would be situated between the cheek and the teeth, the quantity of saliva amassed in the canal of the duct, by its temporary oblitera tion, would flow down and become intimately mixed up with the particles of the food, which would now entirely surround its orifice. This relation, then, of the buccinator with the duct of the parotid would seem to regulate the supply of saliva, which, if this view be correct, flows down only at a time when it can be most thoroughly incorporated with the material during its mastication. The relation of the ducts of the submaxillary and sublingual glands to this process would seem to be of far less importance. The orifices of Wharton's ducts and the sublingual ducts situated behind the incisor teeth, would appear to hold a direct relation only to the primary stage of mastication, that is to say, lubricating with the saliva the larger maSses into which the food is broken up during that process, and probably after its completion, immediately prior to the passage of the whole mass into the stomach.