THE FUNCTIONS OF THE BRAIN STEM 393 



to the muscles of the larynx and bronchi, and to the oesophagus, stomach 

 and intestines, secretory fibres to the stomach and inhibitory fibres to the 

 heart. 



At the upper border of the bulb enter also the fibres of the eighth nerve, 

 carrying important impressions from the organ of hearing and the organ of 

 static sense. These will be in all probability divided or injured in isolating 

 the bulb from the higher portions of the brain. While in connection wit h t he 

 upper portions of the brain, the bulb receives also afferent impressions 

 from the skin of the face, and the mucous membrane of the nose and mouth 

 through the descending branches of the root of the fifth nerve, which pass 

 down superficially to the tubercle of Rolando. When in connection with the 

 cord the medulla receives afferent impressions from the whole surface of tin- 

 body and from all the muscles and joints through the posterior column 

 nuclei. 



The bulbo-spinal animal, i.e. one in whom a section has been carried out 

 at the upper boundary of the medulla, differs from the spinal animal chiefly 

 in the maintenance of the nexus between the visceral functions and the 

 skeleto- motor functions of the body. After removal of all the brain in 

 front of the bulb, the animal still continues to breathe regularly and auto- 

 matically. The blood pressure and the pulse rate remain normal, and all 

 three mechanisms, respiration, pulse rate, blood pressure, may be affected 

 reflexly by appropriate stimuli, or may be altered in consequence of central 

 stimulation of the medulla. 



In addition to the reflex mechanisms of locomotion, which are evident 

 in the spinal animal, the bulbo-spinal animal shows a greater degree of 

 solidarity in its responses. It is easier to evoke movement of all four limbs. 

 In the frog, if the eighth nerve has been left intact, there is a certain power 

 of equilibration left, and the animal when laid on its back tries to right itself 

 and usually succeeds. 



It is in this portion of the central nervous system that have been located 

 the great majority of the so-called centres. By a statement, that the centre 

 of such-and-such movement or function is situated in the medulla, we mean 

 merely that the integrity of the medulla, or certain parts of it, is essential for 

 the carrying out of the function. Every function, for instance, in which 

 impulses passing up the vagus nerves are involved, is necessarily dependent 

 on the integrity of these nerves and their central connections, and, since these 

 are situated in the medulla, the centres for these functions are also located 

 in this region. From a broad standpoint the medulla or bulb may be looked 

 upon as a ganglion, or a collection of ganglia, whose main office is to guard and 

 preside over the working of the mechanisms at the anterior opening of the 

 body ; by means of which food is seized, tasted, taken into the alimentary 

 canal, and finally digested. The respiratory apparatus belongs to the same 

 system and is innervated through the same nerve channels. Hence the 

 various events in alimentation, such as deglutition, vomiting, mastication. 

 or in the allied respiratory functions, such as phonation, coughing, and 

 respiration itself, are endowed with centres in this part of the brain. In 



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