692 OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



of the Spinal nerves. Experiment shows that, when the trunk of the nerve 

 is stretched, pinched, or galvanized, violent motions of the whole tongue, even 

 to its tip, are occasioned ; and also, that similar movements take place after divi- 

 sion of the nerve, when the cut end most distant from the brain is irritated. 

 In regard to the degree in which this nerve possesses sensory properties, there 



Fig. 188. 



The course and distribution of tlie Hypoglossal or Ninth pair of nerves ; the deep-seated nerves of the 

 neck are also seen: 1, the hypoglossal nerve; 2, branches communicating with the gustatory nerve; 3, a 

 branch to the origin of the hyoid muscles ; 4, the descendens noni nerve ; 5, the loop formed with the branch 

 from the cervical nerves ; 6, muscular branches to the depressor muscles of the larynx ; 7, a filament from 

 the second cervical nerve, and 8, a filament from the third cervical, uniting to form the communicating 

 branch with the loop from the descendens noni; 9, the auricular nerve; 10, the inferior dental nerve; 11, its 

 mylo-hyoidean branch ; 12, the gustatory nerve ; 13, the chorda tympani passing to the gustatory nerve ; 

 14, the chorda tympani leaving the gustatory nerve to join the submaxillary ganglion ; 15, the submaxillary 

 ganglion ; 16, filaments of communication with the lingual nerve ; 17, the glosso-pharyngeal nerve ; 18, the 

 pneumogastric or par vagum nerve ; 19, the three upper cervical nerves ; 20, the four inferior cervical nerves; 

 21, the first dorsal nerve ; 22, 23, the brachial plexus; 24, 25, the phrenic nerve; 26, the carotid artery; 27, 

 the internal jugular vein. 



is some difference of opinion amongst physiologists, founded, as it would seem, 

 on a variation in this respect between different animals. Indications of pain 

 are usually given, when the trunk is irritated after its exit from the cranium ] but 

 these may proceed from its free anastomosis with the cervical nerves, which not 

 improbably impart sensory fibres to it. But in some Mammalia, the hypoglossal 

 nerve has been found to possess a small posterior root with a ganglion ; this is the 

 case in the Ox, and also in the Rabbit ; and in the latter animal, Valentin 

 states that the two trunks pass out from the cranium through separate orifices, 

 and that, after their exit, one may be shown to be sensory, and the other to be 

 motor. Hence, this nerve, which is the lowest of those that originate in the 

 cephalic prolongation of the spinal cord generally known as the medulla oblongata, 

 approaches very closely in some animals to the regular type of the spinal nerves ; 

 and though in Man it still manifests an irregularity in having only a single 

 root, yet this irregularity is often shared by the first cervical nerve, which also 

 has sometimes an anterior root only. The Hypoglossal nerve is distributed not 

 merely to the tongue, but to the muscles of the neck, which are concerned in 

 the movements of the larynx ; and the purpose of this distribution is probably 



