284 SPLANCHNOLOGY. 



tion, is arranged in a rounded band, which extends in the inferior 

 region of the tongue from base to apex, a few fibres reaching the 

 hyoid bone. The lingualis transversus lies between the super- 

 ficial and deep layers, intersecting the extrinsic muscles ; its fibres 

 are always intermixed with a quantity of adipose tissue, and form 

 the bulk of the organ. These layers alter the form of the tongue, 

 the superficial tilting the tip upwards ; the inferior curves it 

 downwards ; while the transverse protracts or elongates it. 



The fibres of the intrinsic muscles are regarded by Chauveau 

 and others as prolongations of the extrinsic muscular fibres. 



The mucous membrane is plentifully supplied with glands, 

 simple and compound. The simple are mere follicles, secreting 

 mucus. The compound glands, and certain closed follicles, are 

 found chiefly at the base of the tongue, about the foramen caecum, 

 posterior pillars, and papillae circumvallatae, into which many of 

 their ducts open. 



LINGUAL PAPILLA. 



The mucous membrane covering the under part of the free 

 surface of the tongue is smooth, but as it passes over the borders 

 is assumes a papillary character, and on the dorsum it is covered 

 with papillae, which roughen and give it a velvety appearance. 

 The papillae comprise three varieties : papillae maximae, calici- 

 form, or circumvallate ; mediae, or fungiform ; and minimae, or 

 filiform. 



The papillce circumvallatce, three to five in number, are 

 situated at the back part of the dorsum. They are arranged 

 triangularly, the single one being posteriorly and mesially placed, 

 corresponding to the foramen caecum. These papillae rest in cup- 

 like depressions of mucous membrane, and are inversely conical, 

 with the apex below ; several such papillae may be enclosed in 

 the same calyx. The fungiform papillce are more numerous, 

 and scattered irregularly over the dorsum, being most numerous 

 on the posterior third ; they are attached by a narrow neck, the 

 base being round, free, and often furnished with filiform papillae. 

 The filiform papilla} cover the greater part, but especially the 

 anterior two-thirds of the dorsum, vanishing towards the base. 

 They are simple or compound, the former having one free pro- 

 cess, the latter more than one. Papillae are processes of the 

 cormm of the mucous membrane, containing terminal nerve 

 filaments, numerous in the larger, but difficult to trace in the 



