642 MEDULLA OBLONGATA. [BOOK in. 



frequent results of section of either of them ; and as we have seen, 

 the possession of these parts, in the absence of the cerebral 

 hemispheres, and even of the corpora striata and optic thalami, is 

 sufficient to carry out the most complex bodily movements. ^ 



Since the paralysis of the face seen in cases of hemiplegia from 

 disease of one corpus striatum is on the same side as that of the 

 limbs, it follows that the impulses proceeding along the cranial 

 nerves cross over like those of the spinal nerves; and when the 

 nucleus of origin of such a nerve as the facial is stimulated on one 

 side, the movements which result are on the opposite side. Hence 

 when paralysis of the face occurs on the opposite side to that of the 

 body, it may be inferred that the injury or disease has affected 

 the cranial nerve (or nerves) in a part of its course before 

 decussation has taken place ; and pathological observations support 

 this view, unilateral disease or injury of the pons Varolii not 

 unfrequently involving the facial nerve of the same side in its 

 comparatively superficial course before decussation has taken place, 

 and so causing paralysis of the muscles of the same side of the 

 face as the disease, and the opposite side to the paralysis of the 

 limbs. It is probable that the decussation which we have seen 

 to take place partly in the spinal cord, is gradually completed as 

 the impulses pass through the medulla and pons Varolii. There 

 does not appear to be adequate support for the view of those who 

 maintain that volitional impulses cross suddenly and completely at 

 the decussation of the pyramids. 



Medulla Oblongata. We have so often spoken of this link 

 between the brain and the spinal cord, that it is hardly necessary 

 here to do more than recall the fact, that the majority of the 

 ' centres ' for various organic functions are situated in it. 



These we may briefly recapitulate as follows : The respiratory 

 centre with its neighbouring convulsive centre. The vaso-motor 

 centre. The cardio-inhibitory centre. The diabetic centre, or 

 centre for the production of artificial diabetes. The centre for 

 deglutition. The centre for the movements of the oesophagus 

 and stomach, with its allied vomiting centre. The centre for 

 reflex excitation of the secretion of the saliva, with which may 

 be associated the centre through which the vagus influences the 

 secretion of pancreatic juice, and possibly of the other digestive 

 juices. 



In the frog, as we have urged, p. 610, the medulla is undoubt- 

 edly largely concerned in the coordination of movements, and it is 

 exceedingly probable that in the mammal also a considerable 

 portion of work of this kind falls to its lot. 



