; FUNCTIONS OF THE BRAIN. 817 



accurately determined. Stimuli pass through the internal nasal branches 

 of the trigeminus or olfactory nerves and efferent fibres are found in the 

 nerves coming to the muscles of expiration. 



(/) The Centre for Coughing.— This centre is placed a little above 

 the respiratory centre. The afferent fibres pass to the centre through 

 branches of the pneumogastric, the efferent in the nerves of expiration 

 and in those that supply the muscles that close the glottis. 



(g) Centre for the Movements of Suckling and Mastication.— This 

 centre also has escaped close localization. Afferent paths reach the 

 medulla through the trigeminal and glosso-pharyngeal nerves. The 

 efferent fibres in the case of suction reach the lips through the facial, the 

 tongue through the hypoglossal, and the muscles which depress and 

 elevate the lower jaw through the inferior maxillary division of the fifth 

 nerves. The same nerves are "concerned in the movements of mastication, 

 with the exception that when the food passes within the dental arch the 

 hypoglossal is concerned in the movements of the tongue, and the facial 

 with the buccinator. 



(h) The Centre for the Secretion of Saliva. — This centre lies in the 

 floor of the fourth ventricle. When the medulla is stimulated, if the 

 chorda tympani and glosso-pharyngeal nerves are intact, a profuse secre- 

 tion of saliva is the result, indicating the efferent course of this impulse. 

 Afferent impulses reach the centre through the nerves of taste. 



(i) The Centre for Deglutition. — This, likewise, is located in the 

 floor of the fourth ventricle. The afferent paths reach the centre through 

 the second and third branches of the fifth pair, the glosso-pharyngeal and 

 the pneumogastric. The efferent channels are found in the motor 

 branches of the pharyngeal plexus. 



(k) The Centre for the Dilatation of the Pupil. — This centre, like- 

 wise, lies in the medulla oblongata, the efferent fibres passing partly 

 through the trigeminal nerve and partly in the lateral columns of the 

 spinal cord, as far down as the cilio-spinal region, and from there passing 

 out by the lowest two cervical and the two upper dorsal nerves into the 

 cervical sympathetic. The centre is normally excited in a reflex manner 

 by diminishing the amount of light entering the eye. Its action, together 

 with that of the centre for contracting the pupil, will be referred to 

 subsequently. 



(I) The centre for vomiting is likewise found in the medulla. Its 

 functions have been already described. 



(m) The medulla oblongata, as discovered by Bernard, exerts a 

 certain influence on the glycogenic function of the liver. When, as 

 already described, a puncture is made in the floor of the fourth ventricle 

 in the neighborhood of the origin of the pneumogastric nerve temporary 

 glycosuria appears within an hour or an hour and a half after the 



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