THE CRANIAL NERVES. 495 



of muscular power in the tongue, while its tactile and gustatory sen- 

 sibilities are preserved. In the experiments of Panizza and Longet. 

 the animals after this operation were unable to move the tongue in 

 any direction ; and in mastication it was liable to be caught and 

 wounded by the teeth. It was therefore reduced to a helpless condi- 

 tion, by division of its motor nerves. 



Connection with Mastication and Deglutition. Although the move- 

 ments of the tongue take no direct part in mastication, they are yet 

 essential to its performance, by bringing successive portions of the food 

 between the teeth and removing those which have undergone tritura- 

 tion. In animals which introduce liquids into the mouth by lapping, 

 this act also becomes impossible after section of the hypoglossal nerves. 

 The action of the lingual muscles is practically of so much importance 

 that, according to Longet, it requires great expenditure of time and 

 patience, in keeping animals with paralysis of the tongue, to supply 

 them with sufficient nourishment for the support of life. 



Connection with Articulation. In man, another function performed 

 by the tongue is that of articulation. As the lingual muscles are im- 

 portant for the pronunciation of all consonants except the labials (6, 

 m, p) and the labio-dentals (f, v), as well as for that of the vowels, a, 

 e, i, and y, their paralysis produces a nearly complete incapacity of 

 articulation. In man, disease or injury of the hypoglossal nerve alone 

 is a rare occurrence, and, when it exists, is almost invariably confined 

 to one side. In glosso-labio-laryngeal paralysis, from lesion of the 

 medulla oblongata (p. 445), the disease is of central origin, and affects 

 other muscles as well as those of the tongue. In these cases, however, 

 the imperfect action of the lingual muscles is an early sign ; and when 

 the disease is fully developed and the tongue completely paralyzed, all 

 power of articulation is lost. 



The hypoglossal nerve, accordingly, though one of the simplest of 

 the cranial nerves in its physiological endowments, is important as an 

 aid in mastication and deglutition, and essential for the production of 

 articulate speech. 





