150 HAND-BOOK OF PHYSIOLOGY. 



For, among the experiments made on this point, many have shown that 

 when the accessory nerve is irritated within the skull, convulsive move- 

 ments ensue in some of the muscles of the larynx; all of which, as already 

 stated, are supplied, apparently, by branches of the vagus; and (which 

 is a very significant fact) Vrolik states that in the chimpanzee the internal 

 branch of the accessory does not join the vagus at all, but goes direct to 

 the larynx. 



Among the roots of the accessory nerve, the lower, arising from the 

 spinal cord, appear to be composed exclusively 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 sensory as well 

 as motor fibres. 



\ 



HYPOGLOSSAL NERVE. 



Distribution. The hypoglossal or ninth nerve, or moto lingum, 

 has a peculiar relation to the muscles connected with the hyoid bone, 

 including those of the tongue. It supplies through its descending branch 

 (descenders noni), the sterno -hyoid, sterno- thyroid, and omo -hyoid; 

 through a special branch of the thyro-hyoid, arid 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. 



Functions. The function of the hypoglossal is exclusively motor, 

 except in so far as its descending branch may receive a few sensory fila- 

 ments from the first cervical nerve. 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 paralyzed. 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 deviation in the direc- 

 tion of the protruded tongue; probably because the tongue is so compact 

 and firm that the muscles on either side, their insertion being nearly 

 parallel to the median line, can push it straight forward or turn it for 

 some distance toward either side. 



SPINAL NERVES 



Functions. Little need be added to what has been already said of 

 these nerves (pp. 93 to 97, Vol. II.). The anterior roots of the spinal 

 nerves are formed exclusively of motor fibres; the posterior roots exclu- 

 sively of sensory fibres. Beyond the ganglia, all the spinal nerves are 

 mixed nerves, and contain as well sympathetic filaments. 



