306 THE NERVOUS SYSTEM 



its movements are much modified through its nervous 

 communication with the medulla. Inhibitory fibers pass 

 from there in the vagus nerve, and if that is cut the 

 heart's motion is accelerated. Accelerator fibers from 

 the medulla pass to the heart through the spinal cord and 

 the sympathetic nerves. Their destruction or severance 

 from the center in the medulla slows the heart's beat. The 

 medulla oblongata, then, is a coordinating center for those 

 reflex actions upon which the maintenance of life depends. 



445. Besides its great function as a center for the 

 reflex action connected with the vital processes, the 

 medulla oblongata also acts, like the cord, as a conductor 

 of sensory and motor impressions. Motor fibers from the 

 upper parts of the brain cross in the anterior pyramids 

 of the medulla and descend the cord, to pass out in the 

 anterior roots of spinal nerves. If they are destroyed on 

 the right side above the crossing, paralysis of motion of 

 the left side results ; while section of the fibers on the 

 right side below the crossing will cause paralysis on the 

 right side. 



446. Functions of the Pons Varolii. The pons, besides 

 serving as a passageway for afferent and efferent impulses 

 between the medulla and other parts of the brain, contains 

 imbedded in the bundles of white fibers a number of 

 nuclei of gray matter connected with the roots of cranial 

 nerves, some of the same nerves being also connected 

 with nuclei in the medulla. The pons is to be regarded 

 as both a conductor and a reflex center, and also as a 

 relay center between the cerebellum and the cerebrum. 



447. Functions of the Cerebellum. The cerebellum re- 

 ceives impressions through its three pairs of peduncles 

 by which its hemispheres are connected with other parts 

 of the brain, and so with the spinal cord, and with each 



