428 



SALIVARY GLANDS. 



studded at intervals with elongated or rounded 

 nuclei, which present a great analogy with 

 the fibres of organic muscle, if they be not 

 completely identical with it. We are at pre- 

 sent, however, in doubt as to whether the 

 intermediate membrane of small glands, and 

 of the terminal portion of the large, be really a 

 simple transparent membrane, or whether it 

 acquire, as the tubes which it envelopes en- 

 large, cellular and muscular fibres externally, 

 whilst the previously transparent membrane 

 disappears or remains as a basement mem- 

 brane towards the epithelium ; or whether a 

 separation or splitting of the transparent 

 membrane into fibres takes place. In the 

 opinion of Henle, all the true glands having a 

 vesicular termination, from the smallest to the 

 most complicated, have an intermediate mus- 

 cular tunic, with a series of longitudinal fibres 

 situated within, and circular fibres without, 

 the former being much more highly developed 

 than the latter, and entirely absent in the 

 more delicate ramifications of the duct. Miiller, 

 admitting the great difficulty of determining by 

 the microscope the muscular character of the 

 intermediate coat, is nevertheless of opinion 

 that such is its nature, and appears inclined 

 to believe that the frequent sudden expulsion 

 of the saliva is attributable to it. 



The cellular or areolar tissue forms an in- 

 tricate network throughout the whole struc- 

 ture of the salivary 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 

 rctc for the ramifications of the arteries, veins, 

 and nerves. 



The vascular supply. This is derived from 



Fig. 306. 



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 Jig. 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 Ti-gV<T to TTS o- 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. 



Capillaries of Parotid of Pig. 



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 alternately 

 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 between 

 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 between 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 



