THE HYPOGLOSSAL AND PHRENIC NERVES. 343 



dence of irritation, and also from its origin and distribution. Its action 

 is not essential in ordinary or involuntary respiration. In voluntary res- 

 piration it is brought into play. 



OF THE TWELFTH PAIR, OR HYPOGLOSSAL NERVE. 



This nerve arises in the groove between the pyramidal and olivary 

 bodies, by 8 or 10 filaments, which are collected into two The twelfth 

 bundles. It next passes forward and crosses inward, pur- pair, or hypo- 

 sues a course which is concave upward, and supplies the gossal< 

 genio-hyoglossus and muscles of the tongue generally, giving off the 

 following branches in its course : the descendens noni, the thyro-hyoid, 

 and filaments connecting the gustative nerve. It also anastomoses with 

 the pneumogastric, spinal accessory, first and second cervical nerves, and 

 sympathetic. 



The hypoglossal is the motor nerve of the tongue, irritation of it giv- 

 ing rise to movements throughout that organ, the lingual branch of 

 the fifth being the sensory. The hypoglossal causes the muscles of the 

 neck to aid in the movements necessary for articulate speech. 



ILLUSTRATION OF THE HYPOGLOSSAL NERVE. 



1, medulla oblongata; 2, glosso-pharyngeal ; 3, pneumo- 

 gastric ; 4, superior laryngeal ; 5, spi- 

 nal ; 6, first cervical pair ; 7, second 

 pair ; 8, third pair ; 9, fourth pair ; 

 10, lingual; 11, origin of hypoglos- 

 sal ; 12, anastomosis of hypoglossal 

 with first cervical; 13, anastomosis 

 with nervous loop of two first cervi- 

 cals ; 14, descending branch of hy- 

 poglossal, anastomosing with, 15, de- 

 scending branches of cervical plexus ; 

 16, twig of thyro-hyoid muscle; 17, 

 The hypogiossai nerve, branches of hyoglossus ; 18, recur- 



rent branch of stylo-glossus ; 19, branches of genio-hyoid ; 20, plexiform 

 branches of hypoglossal ; 21, anastomotic branch with the lingual ; 22, 

 branch for submaxillary ganglion ; A, vertebral artery ; B, external car- 

 otid ; C, lingual ; D, temporal ; E, internal maxillary ; #, portion of the 

 condyle of the occipital bone ; , median section of atlas ; c, styloid pro- 

 cess ; d, stylo-glossus ; e, stylo-pharyngeus ; /*, hyoglossus ; <?, genio- 

 glossus ; A, pterygoideus externus ; ?, pterygoideus internus. 



OF THE PHRENIC NERVE. 



Although the phrenic, or internal respiratory nerve is not strictly in- 



