220 OF MASTICATION AND DEGLUTITION. 



339. The lower jaw is connected with the skull by a 

 remarkable articulation, which holds a middle rank 

 between arthrodia and ginglymus, and, being supplied 

 with two cartilaginous menisci of considerable strength, 

 affords an easy motion in every direction. 



The digaster, assisted by the geniohyoidei and mylo- 

 hyodei muscles, draws the lower jaw down, when we 

 open the mouth. 



The masseters and temporal chiefly raise it again 

 when we bite off any thing, and are most powerfully 

 contracted when we break hard substances. 



Its lateral motions are accomplished by the internal 

 and external pterygoid. 



The latter can also draw it forwards. 



340. Substances are retained in the mouth and moved 

 and brought under the action of the teeth by the buc- 

 cinator, and by the tongue which is very flexible and 

 changeable in form. (235) 



341. During manducation, there occurs a flow of 

 saliva,* which is a frothy fluid, consisting of a large 

 portion of water united with some albumen, and hold- 

 ing in solution a small quantity of phosphate of lime 

 the source of the tartar of the teeth and of salivary cal- 

 culi. From being constantly applied to the tongue, it. 

 is insipid, although it contains some microcosmic salt 

 (phosphate of ammonia), as well as muriatic and, inva- 

 riably, a small portion of oxalic, acid. It is antiseptic f 

 and very resolvent. (A) 



* J. Barth. Sicbold, I/istoria Systcmatis Salivalis. Jen. 17D7. 4to. with 

 copper-plates. 



f Fringlc, On the Diseases of the Army. Append, p. XLVIII. L. LXI. sq. Lond. 

 5. 4to. 





