516 DIGESTION. 



tor muscles is the most extensive; but the lateral or grinding motion 

 is practicable to the necessary extent; and the muscles of both kinds 

 have a medium degree of developement. The teeth, likewise, partake 

 of the characteristics of those of the carnivorous and herbivorous 

 animals ; twelve the canine teeth and lesser molares corresponding 

 to those of the carnivorous ; and twenty the incisors and larger mo- 

 lares to those of the herbivorous. 



The tongue must be regarded as an organ of mastication. It rests 

 horizontally on the floor of the mouth ; is free above, anteriorly ; and, 

 to a certain extent, beneath and at the sides. Behind, it is united to 

 the epiglottis by three folds of the mucous membrane of the mouth; 

 and is supported at its base by the os hyoides, with which it partici- 

 pates in its movements. The tongue, as the organ of taste and articu- 

 lation, has been described already (p. 145). We have only, therefore, 

 to describe the os hyoides and its attachment to that bone. The 

 hyoid bone has, as its name imports, the shape of the Greek letter v , 

 the convex part being before. (Fig. 194.) It is situate between the 

 tongue and larynx : and is divided into body or central part ; and into 

 branches, one extremity of which is united to the body by an inter- 

 mediate cartilage, that admits of slight motion ; whilst the other is free, 

 and is called greater cornu. Above the point, at which the branch is 

 articulated with the body, is an apophysis or process, called lesser cornu. 

 The os hyoides is united to the neighbouring parts by fibrous organs, 

 and muscles. The former are; above, the stylo-hyoid ligament, which 

 extends from the lesser cornu of the bone to the styloid process of the 

 temporal bone ; below, a fibrous membrane, called thyro-hyoid, passing 

 between the body of the bone and the thyroid cartilage; and two liga- 

 ments, extending from the greater cornu of the hyoid bone to the thyroid 

 cartilage, called thyro-hyoid. Of the muscles; some are above the hyoid 

 bone, and raise it; viz., the genio- and mylo-hyoideus, already referred 

 to ; the stylo-hyoid, and some fibres of the middle constrictor of the 

 pharynx. Others are below, and depress it. They are the sterno-thyro- 

 hyoideus, omo-hyoideus and sterno-thyroideus. The base of the tongue 

 is attached to the body of the bone by a ligamentous tissue, and by the 

 fibres of the hyoglossus muscle. 



Among the collateral organs of mastication are those which secrete 

 the saliva, and the various fluids which are poured out into the mouth, 

 constituting together what has been termed the apparatus of insali- 

 vation. These fluids proceed from different sources. The mucous 

 membrane of the mouth, like other mucous membranes, exhales a 

 serous or albuminous fluid, besides a mucous fluid secreted by the nu- 

 merous follicles contained in its substance. Four glands likewise exist 

 on each side, destined to secrete the saliva, which is poured into the 

 mouth by distinct excretory ducts. They are the parotid, submaxil- 

 lary, sublingual, and intra-lingual or lingual. The first is situate be- 

 tween the ear and the jaw; and its excretory duct opens into the mouth 

 opposite the second small molaris of the upper jaw. By pressing 

 upon this part of the cheek, the saliva can be made to issue into the 

 mouth, in perceptibly increased quantity. The submaxillary gland is 

 situate beneath the base of the jaw; and its excretory duct opens into 



