THE HYPOGLOSSAL. 579 



was liable to be caught between the teeth and wounded ; an accident 

 which evidently caused suffering to the animal, thus showing the con- 

 tinued sensibility of the paralyzed organ. 



Connection of the Hypoglossal Nerve with Mastication and Degluti- 

 tion. Although the movements of the tongue do not take a direct part 

 in mastication, they are yet of essential importance to its accomplish- 

 ment, by bringing successive portions of the food between the teeth and 

 removing those which have already undergone tritu ration. In species 

 where liquids are introduced into the mouth by the act of lapping, this 

 movement becomes also impossible after section of the hypoglossal 

 nerves ; and both liquid and solid food, the latter already reduced to a 

 pulp, must be introduced far backward into the fauces in order to allow 

 of their deglutition. The natural action of the lingual muscles is prac- 

 tically of so much importance that, according to Longet, it requires a 

 great expenditure of time and patience, in animals with paralysis of the 

 tongue from division of the hypoglossal nerves, to supply them with 

 sufficient nourishment for the support of life. 



Connection of the Hypoglossal Nerve with Articulation. In man, 

 another important function is performed by the tongue as a muscular 

 organ, namely, that of articulation. As the lingual muscles take an 

 important part in the pronunciation of all the consonants except the 

 labials (6, ?n, p} and the labio-dentals (/, v), as well as in that of the 

 vowels a, e, t, and y, their paralysis will necessarily produce a nearly 

 complete incapacity of articulation. In man, disease or injury of the 

 hypoglossal nerve alone is a rare occurrence, and is almost invariably 

 confined to one side. In the glosso-labio-laryngeal paralysis, described 

 in connection with the functions of the medulla oblongata (p. 510), the 

 disease is of central origin, and affects, in various proportions, other 

 muscles as well as those of the tongue. Here, however, according to 

 Hammond, the earliest signs of imperfect action show themselves in the 

 lingual muscles, and when the disease is fully developed the tongue 

 becomes completely paralyzed, and all power of articulation is lost. 



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

 the cranial nerves in the nature of its physiological endowments, is 

 essential for the expression of ideas by articulate language, and is also 

 important as an aid in the mastication and deglutition of the food. 



General Arrangement and Mode of Origin of the Cranial Nerves 



Notwithstanding the apparent irregularity in source and distribution 

 of the cranial nerves, as compared with the spinal, an examination of 

 their internal origin shows that they are arranged on a definite plan, 

 not essentially dissimilar to that of the spinal nerves. The difference 

 between them depends only upon the changed position of the gray 

 substance in the medulla oblongata as compared with that in the spinal 

 cord. When the central canal of the cord opens into the cavity of the 

 fourth ventricle, just above the point of divergence of the posterior 

 columns, the gray matter surrounding it becomes posterior instead of 



