THE MEDULLA OBLOXGATA. 117 



Of the smaller collections of gray substance, probably none has the 

 peculiar interest which the floor of the fourth ventricle possesses 

 for this reason. 



What are the functions of the medulla oblongata ? 



The medulla has practically the same functions as the cord, 

 conduction and reflexion ; but in both these qualities it excels the 

 cord, for in the conduction of impulses it has to transmit all that 

 pass between the brain and spinal system, and in the reflex actions 

 which it originates it is much more elaborate than the cord. The 

 automatic reflex actions of the medulla involve the rhythm of the 

 vital organs, respiration and heart-action. 



How may the functions of the medulla be demonstrated in the 

 frog? 



If the spinal cord be removed up to the medulla, the respirations 

 continue, and in the same way they do not cease if the brain be 

 removed without disturbing this organ, or, if both cord and brain 

 be removed without disturbing the medulla, the movements of 

 breathing will continue. If the medulla is injured at the origin 

 of the pneumogastric nerve, however, the movements of respiration 

 cease and the animal dies. The same occurs when a similar injury 

 occurs in the higher animals and in man. Death occurs instanta- 

 neously in this way when the medulla is broken near the axis in 

 executions by hanging " the neck is broken " or an animal is 

 killed by " pithing " in laboratory experiments. 



What are the special centres in the medulla ? 



There are a considerable number of centres in the medulla 

 which control many important and complicated co-ordinated mus- 

 cular actions. These are centres of reflex action for the most part ; 

 that is, are called upon to act in response to stimuli derived from 

 an afferent impulse or to a voluntary effort. 



What is meant by automatism of the medulla ? 



The impulses which are sent out to muscles without apparent affer- 

 ent stimuli, and without an effort of the will, are called automatic. 

 Such rhythmic impulses as those which maintain the respiratory 

 function belong to this class. It is not to be doubted that such 

 actions are reflex and in response to stimuli. In the case of the 

 lungs, for example, the presence of deoxygenated blood may serve 

 to excite an afferent impulse. Nevertheless, some authors distin- 



