468 ORGAN OF TOUCH. 



follicles rather than sentient organs ; the true sentient papillae being ex 

 tremely minute and occupying their surface, as they do that of the other 

 papillae of the tongue. 



The Papilla fungiformes (p. capitatse) are irregularly dispersed over 

 the dorsum of the tongue, and are easily recognised among the other 

 papillae by their rounded heads and larger size. A number of these papilla3 

 will generally be observed at the tip of the tongue. 



Behind the papilla? circumvallatae, at the root of the tongue, are a num- 

 ber of mucous glands, which open upon the surface. They have been im- 

 properly described as papilla? by some authors. 



Vessels and Nerves. The tongue is abundantly supplied with blood by 

 the lingual arteries. 



The Nerves are three in number, and of large size : The gustatory 

 branch of the fifth, which is distributed to the papillae, and is the nerve of 

 common sensation and taste. The glosso-pharyngeal, which is distributed 

 to the mucous membrane, follicles, and glands of the tongue, is a nerve 

 of sensation and motion ; it also serves to associate the tongue with the 

 pharynx and larynx. The hypoglossal is the motor nerve of the tongue, 

 and is distributed to the muscles. To these may be added the chorda 

 tympani, which conveys a motor influence from the facial nerve to the 

 lingualis muscle. 



The Mucous membrane which invests the tongue, is continuous with 

 the derma along the margin of the lips. On either side of the frsenum 

 linguae it may be traced through the sublingual ducts into the sublingual 

 glands, and along Wharton's* ducts into the submaxillary glands : from 

 the sides of the cheeks it passes through the openings of Stenon'sf ducts 

 to the parotid glands : in the fauces, it forms the assemblage of follicles 

 called tonsils, and may thence be traced downwards into the larynx and 

 pharynx, where it is continuous with the general gastro-pulmonary mucous 

 membrane. 



Beneath the mucous membrane of the mouth are a number of small 

 glandular granules, which pour their secretion upon the surface. A con- 

 siderable number of them are situate<? within the lips, in the palate, and 

 in the floor of the mouth. They are named from the position which they 

 may chance to occupy, labial, palatal glands, &c. 



ORGAN OF TOUCH. 



The S/dn is the exterior investment of the body, which it serves to 

 cover and protect. It is continuous at the apertures of the internal cavities 

 with the lining membrane of those cavities, the internal skin or mucous 

 membrane, and is composed essentially of two layers, derma and epiderma. 



The DERMA or cutis is chiefly composed of areolo-fibrous tissue, besides 

 which it has entering into its structure elastic and contractile fibrous tissue, 

 together with blood-vessels, lymphatic vessels and nerves. The areolo- 

 fibrous tissue exists in greatest abundance in the deeper stratum of the 

 derma, which is consequently dense, white, and coarse ; the superficial 



* Thomas Wharton, an English physician, devoted considerable attention to the ana- 

 l')mv of the various glands; his work, entitled " Adenographia," &c., was published in 

 1656. 



f Nicholas Stenon, a Danish anatomist : he was made professor in Copenhagen in 

 1672. 



