728 NERVOUS SYSTEM. 



When we see that frogs will live for weeks, and sometimes for months, after destruc- 

 tion of the medulla oblongata, and that, in mammals, by keeping up artificial respiration, 

 we can prolong many of the most important functions, as the action of the heart, for 

 hours after decapitation, we can understand the physiological absurdity of the proposition 

 that there is any such thing as a vital point, in the medulla or in any part of the nervous 

 system. 



Connection of the Medulla Ollongata with Various Reflex Acts. There are numerous 

 reflex phenomena that are completely under the control of the medulla oblongata as a 

 nerve-centre. Among these are the various acts connected with respiration, as yawning, 

 coughing, crying, sneezing, etc. It also presides over the coordination of the muscles 

 concerned in expression, and the act of vomiting. We have seen, in treating of the 

 pneumogastric nerves, that their galvanization arrests the action of the heart in diastole. 

 The same result follows galvanization of the medulla at the point of origin of these nerves. 

 We have also fully discussed the influence of the medulla upon sugar-formation in the 

 liver, as illustrated by the striking experiments of Bernard, in which he produced diabetes 

 in animals by irritating the floor of the fourth ventricle, and the influence of this centre 

 upon the quantity and the composition of the urine. 



There is very little to be said concerning certain ganglia and other parts of the brain 

 that we have not yet considered. The olfactory bulbs, or ganglia, preside over olfaction 

 and will be treated of fully in connection with the special senses. The pineal gland and 

 the pituitary body, in their structure, present a certain resemblance to the ductless glands, 

 and their anatomy has been considered in another chapter. Passing over the purely 

 theoretical views of the older writers, who had very indefinite ideas of the functions of 

 any of the encephalic ganglia, we have only to say that the uses of the pineal gland and 

 pituitary body in the economy are entirely unknown. The same remark applies to the 

 corpus callosum, the septum lucidum, the -ventricles, hippocampi, and various other minor 

 parts that are necessarily described in anatomical works. It is useless to discuss the 

 early or even the recent speculations with regard to the functions of these parts, which 

 are entirely unsupported by experimental or pathological facts and which have not ad- 

 vanced our positive knowledge. Most of the parts just enumerated have no physiological 

 history. 



Rolling and Turning Movements following Injury of Certain Parts of the 



Eneephalon. 



The remarkable movements of rolling and turning, produced by section or injury of 

 certain of the commissural fibres of the encephalon, are not very important in their bearing 

 upon the functions of the brain, and they are rather to be classed among the curiosities of 

 experimental physiology. These movements follow unilateral lesions and are dependent, 

 to a certain extent, upon a consequent inequality in the power of the muscles on one side, 

 without actual paralysis. Vulpian enumerates the following parts, injury of which, upon 

 one side, in living animals, may determine movements of rotation : 



" 1. Cerebral hemispheres; 



" 2. Corpora striata ; 



" 3. Optic thnlami (Flourens, Longet, Schiff); 



" 4. Cerebral peduncles (Longet) ; 



" 5. Pons Varolii ; 



" 6. Tubercula quadrigemina or bigemina (Flourens) ; 



" 7. Peduncles of the cerebellum, especially the middle, and the lateral portions of the 

 erebellum (Magendie) ; 



" 8. Olivary bodies, restiform bodies (Magendie) ; 



" 9. External part of the anterior pyramids (Magendie) ; 



