Functions of the Cerebellum. 617 



Another effect on the heart is the inhibitory or retardatory action 

 which comes through the vagus nerve. The excitement in the vagus 

 nucleus, which thus overflows to the heart, may be induced by powerful 

 irritation of the sensory ( afferent ) nerves generally, as when a person 

 suddenly tumbles into cold water ; or of the sensory branches of the 

 fifth pair in the nostrils, or of the sensory nerves in the larynx, and 

 particularly of the intestinal sensory nerves. ( See chap. 53. ) There 

 are also "mental states," that is, conditions of the cerebrum which 

 stimulate the retardatory centers. 



The medulla is also a co-ordinating center for the reflex associated 

 movements of the limbs, and the muscles of different parts which act 

 "together and in harmony for a definite end, when the influence of the 

 cerebrum is cut off, and the subject, therefore, in a state of insensibil- 

 ity, and also those movements, such as swallowing, which are constantly 

 being performed by associated action, without the supervision of the 

 will, and often in opposition to it. The muscles of the face are also 

 subject to regulation and control through the medulla oblongata. It is 

 the various degrees of contraction of the different muscles of the face 

 that give what is called expression. An action of a certain sort, in the 

 stomach, for example, sends a current to the medulla, from which it 

 overflows to the muscles numbered 12 and 21 (and others) in fig. 66, 

 and gives what we have learned by observation to be expression of pain. 

 Another, irritation on the bottom of the foot, as with a feather, sends 

 up a current which becomes reflected to muscles 9, 22, 23, &c. , giving 

 an expression of laughing. Different conditions in various parts of the 

 body, constantly send up their stimuli to the medulla, from which they 

 .are reflected to muscles not only in the face but in all parts of the body, 

 causing contractions of the muscles in first one part and then another, 

 which give rise to the innumerable unconscious movements of the limbs, 

 and the postures, gestures, tricks, mannerisms, smirks and grimaces, 

 that we are performing every moment of our waking hours. The power 

 which runs all this machinery is not generated in the nerve centers, but 

 only balanced and co-ordinated there. 



CHAPTER LXI. 



FUNCTIONS OP THE CEREBELLUM. 



The large amount of vesicular brain matter in the cerebellum, marks 

 this organ as a great laboratory of nervous stimulation, condensing 

 inan}^ simultaneous stimuli, so that a single resultant motor action may 

 follow, and dispersing other single stimuli into many channels, by which 

 as many different motor actions are set up or modified. The cerebellum 



