THE APPABATUS OF TASTE. 923 



pharyngeal, distributed to the superior third of the tongue, 2. The lingual 

 branch of the fifth, distributed to the anterior two-thirds. 3. Filaments from 

 the chorda tympani.) 



The tongue and its investing membrane having been described at p. 400, 

 their anatomy need not again be referred to : but we must glance at the organi- 

 zation of the latter, in considering it as the special apparatus of gustation. This 

 will necessitate a few words with regard to tlie free surface of the membrane 

 which comes into c^^tact witli the sapid bodies, and some considerations on the 

 terminations of the nerv< iiicl' transmit the impressions produced by these 

 bodies to the brain. 



Free Surface of the Lingual Mucous Membrane. — This surface is 

 studded by a multitude of papillary prolongations, which are nearly all limited 

 to the upper surface of the tongue, to which they give a tufty appearance. 

 Their form and volume, as mentioned at p. 402, are very variable, according to 

 situation : some are microscopic, while others form voluminous caruncles ; 

 othfci's, again, are long, conical, and filiform ; another variety is round or 

 depressed, representing a hemispherical tubercle scarcely projected beyond the 

 general surface, or placed at the bottom of an excavation in the mucous mem- 

 brane. The latter constitute the circumvaUate papillae (p. circumralato', p. 

 lent icida res), and are considered the true organs of gustation ; the others are 

 the fungiform {p. rapitat(c) a,nd filiform papilke, which play a mechanical part on 

 the surface of the tongue. 



The circumvaUate papill(B in the Horse are two in number, and situated near 

 the base of the tongue ; their diameter is so considerable that they have been 

 named the blind or caecal openings {taste-pores). They are the principal, but 

 not the only organs of taste. Their surface is mammillated, each prominence 

 corresponding to a single papilla, and being placed below the level of the raised 

 border encircling them. A deep fossa surrounds them, and limits at their base 

 a pedicle, which unites them to the other portions of the mucous membrane (see 

 Figs. 218, 219). 



The circumvaUate papillae show, around their peduncle, a band of adenoid 

 tissue ; and in their substance conglomerate glands, as in other parts of the 

 mucous membrane. They are covered by an epithelium containing some 

 scattered pigment-granules, the thickness of which is much diminished at the 

 bottom of the fossa circumscribing them. 



Termination of the Gustatory Nerves. — The hypoglossal is the motor 

 nerve of the tongue, the lingual the nerve of general sensibility, and the chorda 

 tympani and glosso-pharyngeal the filaments of special sensibility : this appears 

 to be clearly ascertained from the recent experiments and observations of Lussana. 

 The lingual branch of the glosso-pharyngeal nerve gives gustatory sensibility to 

 the posterior third of the tongue ; the chorda tympani to the anterior two-thirds. 



The gustatory nerves present — as do all those of the organs of sense — a par- 

 ticular mode of termination. First indicated by Axel Key, their special manner 

 of terminating has been carefully studied by Lowen, Schwalbe, and Ranvicr. 

 According to these anatomists, the terminal nerve-tubes lose their medullary 

 envelope, and, reduced to their axis-cylinder, are thrown out in small oval masses 

 which might be termed gustatire bulbs {taste-buds, or taste-goblets). Sartoli and 

 Ranvier have seen some directly enter the epithelium around the bulbs. The 

 gustatory bulbs are more particularly placed around the pedicles of the calyciform 

 papillae, in the substance of the epithelium. They are fusiform, their inner 



