THE HYPOGLOSSAL NERVE. 565 



no other means than that of experiment by which the diffi- 

 culty may be solved. It is, however, certain that the 

 accessory nerve does not supply all the motor filaments 

 which the branches of the pneumogastric contain; for 

 division of the pneumogastric produces a much more ex- 

 tensive paralysis of motion in all the parts that it supplies, 

 than division of the accessory or its internal branch does, 

 especially in regard to the larynx, and other respiratory 

 organs : almost the only effects of destruction of the acces- 

 sory are loss of voice, and panting in great efforts (Ber- 

 nard). 



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 linguce, 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 an} r 



