578 THE CRANIAL NERVES. 



cles). The trunk of the nerve also receives communicating filaments 

 from the first and second cervical spinal nerves, which, according to 

 Cruveilhier, are filaments of reenforcement, accompanying the hypo- 

 glossal nerve toward its peripheral termination. 



Physiological properties of the Hypoglossal Nerve. The motor char- 

 acter of the hypoglossal nerve is easily established by the results which 

 follow its irritation and division. If the nerve be exposed in the living 

 or recently killed animal at the top of the neck, where it runs parallel 

 to and a little above the hyoid bone, pinching or wounding its fibres, or 

 the application of the galvanic stimulus, produces immediately convul- 

 sive action of the muscles of the tongue. The same effect follows if the 

 trunk of the nerve be divided at this point, and the irritation applied to 

 its peripheral extremity ; showing that the contractions thus produced 

 are not due to reflex action, but to a direct stimulus conveyed through 

 the hypoglossal nerve to the muscular fibres. The excitability of the 

 nerve is consequently beyond question. Whether it possess also any 

 sensitive fibres of its own is not so certain. Longet obtained in this 

 respect only negative results ; the division of the filaments of origin of 

 the nerve, in his experiments on dogs, through the space between the 

 occiput and the atlas, not producing perceptible signs of pain. The 

 trunk of the hypoglossal nerve outside the cranial cavity, certainly pos- 

 sesses some degree of sensibility, according to the testimony of nearly all 

 experimenters ; but this is regarded as derived, like that of other motor 

 nerves, from inosculations beyond its point of origin, especially from 

 those of the first and second cervical spinal nerves near the base of 

 the skull, and from branches of the fifth pair near its terminal distri- 

 bution. Whatever sensibility it may possess is destined only for the 

 muscular substance of the tongue, and not for its mucous membrane; 

 since, in the first place, division of the lingual branch of the fifth pair 

 and of the glossopharyngeal nerve destroys both tactile and gustatory 

 sensibility over the whole surface of the tongue, though the hypoglossal 

 be left untouched ; and secondly, according to the experiments of Lon- 

 get, after division of both hypoglossal nerves in the dog the surface of 

 the tongue, when touched with the point of a needle, evinces its ordinary 

 tactile sensibility, the application of bitter solutions causes signs of dis- 

 gust, and the contact of foreign bodies at the base of the organ excites 

 the action of vomiting. 



The distinct and uniform result of section of both hypoglossal nerves 

 is a loss of muscular power in the whole substance of the tongue, while 

 its tactile and gustatory sensibilities are preserved. In the experiments 

 of Panizza, confirmed by those of Longet, the animals upon which this 

 operation had been performed were unable to move the tongue in any 

 direction, or even to restore it to its natural position when it was turned 

 back, except by hanging the head downward and shaking it, thus allow- 

 ing the organ to fall forward by its own weight, as a helpless mass. In 

 the movements of the jaws, which were not interfered with, the tongue 



