THE MEDULLA OBLONGATA. 195 



nerve centers presiding over different functions, some of which are 

 as follows viz. : 



1. A center which controls the movements of mastication, through 

 afferent and efferent nerves. 



2. A center reflecting impressions which influence the secretion of 

 saliva. 



3. A center for sucking, mastication, and deglutition, whence are 

 derived motor stimuli exciting to action and coordinating the 

 muscles of the palate, pharynx, and esophagus, necessary for the 

 swallowing of the food. 



4. A center which coordinates the muscles concerned in the act of 

 vomiting. 



5. A speech center, coordinating the various muscles necessary for 

 the accomplishment of articulation through the hypoglossal, facial 

 nerves, and the second division of the fifth pair. 



6. A center for the harmonization of muscles concerned in expression, 

 reflecting its impulses through the facial nerve. 



7. A cardiac center, which exerts (i) an accelerating influence over 

 the heart's pulsations through accelerating nerve-fibers emerging 

 from the cervical portion of the cord, entering the inferior cervical 

 ganglion, and thence passing to the heart ; (2) an inhibitory or 

 retarding influence upon the action of the heart, through fibers 

 of the spinal accessory nerve running in the trunk of the pneumo- 

 gastric. The cardio-inhibitory center is in a state of tonic activity 

 and continuously sends impulses to the heart which exert an in- 

 hibitory influence upon its action. It may be stimulated directly 

 by anemia as well as by venous hyperemia of the blood-vessels 

 of the medulla and increased venosity of the blood. It is excited 

 reflexly by the stimulation of the central end of the vagus, sciatic, 

 and splanchnic nerves. 



8. A vaso-motor center, which, by alternately contracting and dilating 

 the blood-vessels through nerves distributed in their walls, regu- 

 lates the quantity of blood distributed to an organ or tissue, and 

 thus influences nutrition, secretion, and calorification. The vaso- 

 motor center is situated in the medulla oblongata and pons Varolii, 

 between the corpora quadrigemina and the calamus script orius. 

 The vaso-motor fibers having their origin in this center descend 

 through the interior of the cord, emerge through the anterior 

 roots of spinal nerves, enter the ganglia of the sympathetic, and 

 thence pass to the walls of the blood-vessels, and maintain an 



