THE ESSENTIAL PHENOMENA OF DIGESTION. 



33 



FIG. 



penetrate to a cavity in the centre of the tooth, which is 

 filled by a soft substance called the pulp. 



The tongue is a muscular organ attached to the pos- 

 terior portion of the floor of the mouth. Perfectly free 

 in front, and endowed with extreme mobility, it aids 

 in the perception of 

 tastes, in the forma- 

 tion of the voice, and 

 in deglutition or swal- 

 lowing. Its surface 

 is covered with a di- 

 gestive mucus that 

 furnishes useful in- 

 dications to the phy- 

 sician. Indeed, since 

 all parts of the diges- 

 tive mucus are in 

 close sympathy with 

 each other, and ordi- 

 narily participate in 

 the same affections, 

 the condition of the 

 tongue usually indi- 

 cates in a positive 

 manner a corre- 

 sponding condition 

 of the stomach and 

 other portions of the 

 digestive canal. 



There are six salivary glands, symmetrically arranged, 

 three on each side of the face. The largest are the 

 parotid glands, and are situated in front of the ears in 

 ^he thickness of the cheeks ; the maxillary glands are 



VERTICAL SECTION OF THE HEAD AND NECK. 

 c, cavity of skull; /, falx; s, spinal canal, 

 leading from cavity of skull ; n, right nasal 

 cavity. Below the hard and soft palate: t, 

 tongue; p, pharynx; o, oasophagus; e, epi- 

 glottis ; I, larynx. 



