THE HEAD AND NECK 1247 



root of the tongue, in the region of the epiglottis ; and (5) the hypo- 

 glossal nerve, which supplies the lingual muscles. 



Sympathetic filaments are also conducted to the tongue by the 

 various arteries. 



Taste-buds. — These constitute the gustatory organs. They are 

 modified epitheUal cells, and are present in the following situations : 

 (i) The sides of the circumvallate papillae, and the opposed surface 

 of each vallum ; (2) the sides of the anterior two-thirds of the tongue, 

 partly in connection with the fungiform papillae, and partly em- 

 bedded in the stratified epitheHum; (3) the folds which form the 

 papules foliates ; {4) the buccal surface of the soft palate ; and (5) the 

 posterior surface of the epiglottis. They extend vertically through 

 the epithehum from the free siuface to the corium of the mucosa. 



Each taste-bud is a flask-shaped body. The base rests upon the 

 corimn of the mucosa, and gives passage to nerve-fibres. The apex 

 or narrow end lies between the surface-cells of the epithehum, and 

 it is perforated by a minute opening, called the gustatory pore, 

 through which the peripheral processes of the gustatory cells in the 

 interior of the bud project as gustatory hairs. 



Structure. — The wall of a taste-bud is composed of flattened, 

 nucleated, epithehal cells, called the sustentacular or tegmental 

 cells. These cells are elongated in the direction of the bud, they 

 taper at either end, emd their margins are closely applied to each 

 other. The interior of the bud consists of a bundle of gustatory cells. 

 Each gustatory cell is nucleated and spindle-shaped. The body of 

 the cell is prolonged, at either end, into a process — peripheral and 

 central respectively. The peripheral process passes to the gustatory 

 pore at the apex of the bud, through which it projects as a gustatory 

 hair. The central process passes towards the base of the bud, which 

 rests upon the corium of the mucosa. It is usually branched, and 

 terminates in free extremities. It does not therefore become con- 

 tinuous with ner\'e-fibres, and therein it differs from the correspond- 

 ing process of an olfactory cell. 



The base of each taste-bud, as stated, gives passage to nerve-fibres. 

 The fibres, as they enter the bud, lose their medullary sheaths, and 

 their axons terminate within the bud in arborizations around the 

 constituent gustatory ceUs. Nerve-fibrils also enter the epithehal 

 wall of the bud, and remiify between the sustentacular or tegmental 

 cells. 



Development. — ^The tongue is developed in the floor of the pharynx in t\vo 

 parts — buccal and pharyngeal — which are separated from each other by the 

 foramen caecum and V-shaped sulcus terminalis. 



The buccal or papillary part, which represents the anterior two-thirds, is 

 developed from the ventral ends of the first or mandibular visceral arch, on 

 either side of the tuberculum impar. It is therefore originally in two parts, 

 right and left, which subsequently fuse and envelop the tuberculum impar. 

 This eminence may give rise to the portion of the buccal part directly in front 

 of the foramen caecum. 



The pharyngeal or basal part of the tongue, which represents the posterior 

 one-third, behind the foramen caecum and sulcus terminalis, is developed from 



