182 DIGESTION. [CHAP. xxm. 



similar height, and in an uninterrupted row, so the articulation of the 

 jaw is intermediate between those of the animal and vegetable feeder. 

 The transverse condyle is received into the glenoid cavity, and in the 

 slighter movements of mastication and articulation does not leave it ; 

 but when the grinding teeth are used, or the mouth is opened wide, 

 the condyle leaves the cavity, and slides forwards for nearly an inch 

 on the prominent root of the zygoma. In the latter action the axis 

 of motion is not in the condyles, but a little above the angle of the 

 jaw, and the joint is arthrodial. A similar advance of the condyles 

 may occur with the mouth nearly closed, the lower incisors being 

 then carried to a level with, or even beyond the upper ones. By 

 the advance of one condyle a partial rotation is effected, the centre 

 of motion being in the other condyle ; and when this is performed al- 

 ternately by both sides, together with an elevation of the jaw, the 

 lower molars are moved laterally over the upper, so as to powerfully 

 grind any intervening substance. The temporal, masseteric, and in- 

 ternal pterygoid muscles more or less directly close the jaw. The 

 hinder fibres of the temporal and masseter carry it also backwards, 

 while the main part of the masseter, and especially the internal pte- 

 rygoid, advance it. Both pterygoid s carry it to the opposite side, 

 chiefly by advancing its ramus, the centre of motion being then in 

 the opposite joint. The external pterygoid neither raises nor de- 

 presses it. The depression of the jaw in mastication seems to be 

 performed solely by the digastric ; and it may be conjectured that 

 even this muscle acts chiefly in its anterior belly, which, unlike the 

 posterior, is supplied by the inferior maxillary nerve, the same which 

 is distributed to the other muscles of mastication. 



Of Insalivation. The salivary organs consist of glands opening 

 into the mouth and pharynx, and furnishing a peculiar fluid which 

 is there mixed with the food and carried down with it to the stomach. 

 The principal are the parotid, submaxillary, and sublingual ; and to 

 these may be added a multitude of small detached glands of similar 

 structure, and probably yielding a similar fluid, scattered under the 

 mucous membrane of the lips, cheeks, soft palate, and parts of the 

 pharynx. The duodenal glands, comprising the pancreas and the 

 glands of Brunner, which have much in common with the salivary 

 glands, will be described at a subsequent page. 



The salivary glands need not here be severally described. The 

 parotid is remarkable for its proximity to the temporo-maxillary ar- 

 ticulation, and some have attributed its greater activity during mas- 

 tication to the pressure to which it is supposed to be then subjected ; 

 but besides that the fact of pressure may be doubted, so mechani- 



