344 THE DIGESTIVE SYSTEM 



The Lymphatics. The lymphatics form a superficial set of small 

 vessels and tissue spaces beneath the epithelial layer, which are espe- 

 cially abundant in the region of the lingual tonsil at the base of the 

 tongue. The lymphatic vessels of this superficial plexus frequently 

 encircle the lymphoid nodules, A deeper plexus of lymphatics in the 

 loose connective tissue of the submucosa receives the lymph from the 

 superficial plexus and conveys it by efferent lymphatic vessels to the 

 deep cervical lymphatic glands. 



The Nerve Supply. The nerve supply of the tongue comprises 

 cerebral, both sensory and motor fibers, and sympathetic fibers. The 

 sympathetic elements supply the glands and blood-vessels ; small ganglia 

 occur along their course. The motor fibers supplying the striped muscle 

 are derived from the hypoglossal nerve. These end in motor end- 

 piates. The sensory fibers arise from the lingual branch of the tri- 

 geminal and the glossopharyngeal nerves. These mediate both general 

 sensibility and the sensation of taste. The fibers which receive the 

 stimuli of general sensibility end as naked varicose fibrils in the con- 

 nective tissue of the body of the tongue, and in the submucosa of 

 the papillae. They are accompanied by small ganglia. Certain fibers 

 also end in muscle spindles. The fibers of special gustatory sensation 

 are also distributed to the papillae; the chorda tympani (branch of 

 the facial) component of the lingual branch of the trigeminal supplying 

 the anterior two-thirds, the glossopharyngeal the posterior one-third of 

 the tongue. At the base of the tongue small nerve bundles of taste 

 fibers are distributed to the circumvallate papillae, and form a subepi- 

 thelial plexus from which fibrils are distributed: (1) to the interior 

 of the taste buds where they end in relation with the gustatory cells, 

 intrag emmal fibers; (2) to the surface of the taste buds, perigemmal 

 fibers; and (3) to the intervening portions of the epithelial layer, where 

 they end between the epithelial cells as in other parts of the tongue, 

 intergemmal fibers (Fig. 175, page 1G1). The taste buds of the soft 

 palate are innervated through the palatine nerves (great superficial 

 petrosal component) of the trigeminal. 



THE ALIMENTARY CANAL 



GENERAL CHARACTERISTICS OF THE WALLS 



It is convenient to consider collectively under this head the pharynx, 

 esophagus,, stomach., and the small and large intestines. This tract 



