THE HYPOGLOSSAL NERVE. 565 



does not join the pneumogastric at all, but goes direct to 

 the larynx. On the whole, therefore, although in some of 

 the experiments no movements in the larynx followed 

 irritation of the accessory nerve, yet it may be concluded 

 that this nerve gives to the pneumogastric some of the 

 motor filaments which pass, with the laryngeal branches, 

 to the muscles of the larynx, especially to the crico-thyroid 

 (Bernard) ; although it is certain that the accessory nerve 

 does not supply all the motor filaments which the branches 

 of the pneumogastric contain. 



Among the roots of the accessory nerve, the lower, 

 arising from the spinal cord, appear to be composed ex- 

 clusively of motor fibres, and to be destined entirely to the 

 trapezius and sterno-mastoid muscles ; the upper fibres, 

 arising from the medulla oblongata, contain many sensitive 

 as well as motor fibres. 



Physiology of the Hypoglossal Nerve. 



The hypoglossal or ninth nerve, or motor lingua-., has a 

 peculiar relation to the muscles connected with the hyoid 

 bone, including those of the tongue. It supplies through 

 its descending branch (descendens noni), the sterno-hyoid, 

 sterno-thyroid, and omo-hyoid ; through a special branch 

 the thyro -hyoid, and through its lingual branches the 

 genio-hyoid, stylo-glossus, hyo-glossus, and genio-hyo- 

 glossus and linguales. It contributes, also, to the supply 

 of the submaxillary gland. 



The function of the hypoglossal is, probably, exclu- 

 sively motor. As a motor nerve, its influence on all the 

 muscles enumerated above is shown by their convulsions 

 when it is irritated, and by their loss of power when it is 

 paralysed. The effects of the paralysis of one hypoglossal 

 nerve are, however, not very striking in the tongue. 

 Often, in cases of hemiplegia involving the functions of 

 the hypoglossal nerve, it is not possible to observe any 



