THE CRANIAL NERVES 681 



VIII. The auditory, or nerve of hearing, by its cochlear root mediates 

 auditory sensations (cf. Fig. 199) and by the vestibular root (cf. page 473) 

 the various functions of the semicircular canals and otolith sacs. 



Various experimental observations indicate that the vestibular root prob- 

 ably has no significance whatever for the auditory sensations. Since the eighth 

 cranial nerve therefore is at least not exclusively auditory in function, J. R. 

 Ewald has proposed that it be simply called the eighth nerve (N. octavus). 



IX. The glossopliaryngeal conveys, besides some motor fibers to the tongue 

 and pharynx, secretory fibers to the parotid glands (cf. page 257) and vaso- 

 dilator fibers to the anterior pillars of the fauces and tonsils. Among its 

 afferent fibers are the taste fibers, also sensory fibers for the mucous mem- 

 brane of the tympanic cavity and Eustachian tube. 



X. The vagus, or pneumo gastric, and 



XI. The spinal accessory. 



In view of the fact that these two nerves are intimately related anatomi- 

 cally and that diverse views are held as to the share each takes in controlling 

 the organs innervated by them, it is most profitable to consider them, as Gross- 

 man has proposed, as one nerve composed of three bundles named, in order 

 of their exit from the medulla, the upper, middle and lower. The upper 

 bundle can readily be separated in the monkey and in man from the glosso- 

 pharyngeal. The lower bundle is the outer branch of the spinal accessory 

 which innervates the trapezius and the sterno-cleido-mastoid muscles. There 

 remains then the trunk composed of the vagus and the inner or true accessory 

 branch in which are to be distinguished an anterior and a middle portion. 



According to the experimental results of Kreidl on the monkey, motor 

 nerves pass in this anterior portion (the vagus of anatomists) to the 

 palatoglossal and palatopharyngeal muscles as well as to the constrictors of 

 the pharynx and oesophagus. Moreover, it is here that the motor fibers 

 of the superior laryngeal are found, also the afferent pulmonary fibers which 

 assist in the automatic regulation of respiration, and in the rabbit, dog and 

 cat at least, the depressor fibers (Fuchs, Codman; cf. page 193). 



In the middle bundle (accessory of the anatomists) are the inhibitory 

 fibers of the heart (cf. page 188), the motor fibers for the levator palati and 

 the motor fibers contained in the inferior laryngeal nerve. 



In the trunk of the vagus are the following fibers, the origin of which is not 

 fully known: (1) efferent fibers, a. To the circulatory organs: accelerator fibers 

 to the heart (page 191) ; vasoconstrictor fibers for the heart, the stomach, intes- 

 tine, kidneys, spleen, and possibly the lungs (page 240) ; vasodilator fibers for the 

 coronary vessels and the lungs (page 235). b. Digestive organs: motor nerves 

 for the stomach (page 284), the small intestine and the upper part of the large 

 intestine (page 289) ; inhibitory fibers for the cardiac sphincter of the stomach 

 and the longitudinal muscles of the small intestine (pages 284, 289) ; secretory 

 nerves for the gastric mucosa and the pancreas (pages 263, 269). c. Respiratory 

 organs: motor and possibly inhibitory fibers for the bronchial muscles (page 324). 



(2) Afferent fibers. Respiratory organs: afferent fibers from the larynx 

 (page 330). 



XII. The liypoglossal innervates the musculature of the tongue. 



