494 THE NERVOUS SYSTEM. 



hyoglossal muscles having lost its power, while the other remains 

 active, the point of the tongue, when protruded, deviates toward the 

 paralyzed side. 



After leaving the medulla oblongata, the fibres of the hypoglossal 

 nerve become parallel with each other, and, passing through the ante- 

 rior condvloid foramen, emerge from the skull in the form of a cylin- 

 drical cord. Immediately beyond this point it presents one or two 

 branches of communication with the pneumogastric, where it crosses 

 the track of this nerve. According to Cruveilhier, these branches con- 

 sist of fibres from the hypoglossal nerve which join those of the pneu- 

 mogastric, and run with them in a peripheral direction. The hypo- 

 glossal nerve then passes downward, nearly to the level of the hyoid 

 bone, where it curves forward, giving filaments to the styloglossal and 

 hyoglossal muscles, and to those immediately beneath the hyoid bone ; 

 after which it turns upward, penetrating the tongue from below, inos- 

 culates with the lingual branch of the fifth pair, and is finally distributed 

 to the muscles of the tongue. It, therefore, animates not only the lin- 

 gual muscles proper, but also those which draw the tongue backward 

 and upward (styloglossal), and backward and downward (hyoglossal 

 and infrahyoid muscles). It also receives filaments from the first and 

 second cervical nerves, which, according to Cruveilhier, are fibres of 

 reinforcement, accompanying the hypoglossal nerve to its peripheral 

 termination. 



Physiological Properties of the Hypoglossal Nerve. The motor 

 character of this nerve is easily established by the results of its irrita- 

 tion and division. If it be exposed, either in the living or the recently- 

 killed animal, where it runs parallel to and a little above the hyoid 

 bone, its irritation produces immediate convulsive action of the tongue. 

 The same effect follows irritation applied to the peripheral extremity 

 of the divided nerve ; showing that the contractions thus produced are 

 not reflex, but due to a direct stimulus conveyed through the nerve to 

 the tongue. Whether the nerve possess also sensitive fibres of its 

 own is not certain. Longet obtained in this respect only negative 

 results ; the division of the nerve roots in dogs, between the occiput 

 and the atlas, not producing perceptible signs of pain. Outside the 

 cranial cavity, according to nearly all experimenters, it possesses some 

 degree of sensibility; but this is probably derived, by inosculation, 

 from the first and second cervical nerves near the base of the skull, and 

 from branches of the fifth pair near its terminal distribution. Whatever 

 sensibility it may possess is destined only for the muscular substance 

 of the tongue, and not for its mucous membrane ; since division of the 

 lingual branch of the fifth pair and of the glossopharyngeal nerve 

 destroys sensibility over the whole surface of the organ, though the 

 hypoglossal be untouched ; and secondly, the tongue evinces its ordi- 

 nary sensibility, according to Longet, after the division of both hypo- 

 glossal nerves. 



The uniform result of section of both hypoglossal nerves is loss 



