HYPOGLOSSAL, .NERVE. 531 



final result, because the muscles of the larynx are paralyzed, 

 and closure of the glottis is impossible. A change in voice fol- 

 lows the section or injury of even one inferior laryngeal, as may 

 often be seen in man from the effect of the pressure of an aneurism. 



IX. HYPOGLOSSAL NERVE. 



This nerve appears in the furrow between the olivary body 

 and the anterior pyramid, on a line with the anterior roots of 

 the spinal nerves. It corresponds with the anterior roots in 

 function, being a purely motor nerve. It bears impulses to the 

 muscles of the tongue and the other muscles attached to the hyoid 

 bone. 



Some sensory fibres lie in its descending branch, but these prob- 

 ably are derived from the vagus or trifacial nerves, with which its 

 branches inosculate. 



It is also said to contain the vaso-motor fibres of the tongue. 



Section of the nerve causes paralysis of the muscles of the 

 tongue ; when this is unilateral, the tongue inclines to the injured 

 side, while being protruded from the mouth ; but while being 

 drawn in, it passes to the sound side. This is easily understood 

 when it is borne in mind that the two acts depend upon the in- 

 trinsic muscles of the tongue, bringing about an elongation or 

 shortening of the organ respectively. 



