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ADVANCED PHYSIOLOGY 



spinal cord pass immediately to the other side and ascend 

 there. Curiously enough, however, an injury destroys the 

 power of voluntary motion on the same side as the injury, 

 but not on the other. Hence messages from the brain pass 

 down the cord on the same side as that to which they finally 

 go. Figure 156 shows these facts diagrammatically. These 

 messages from the brain going down the cord cross over from 

 left to right and vice versa, higher up, mainly in the me- 

 dulla, so that all messages going to either side of the body 

 start from the other side of the brain. Thus, the sensations 

 and motions of each side of the body are connected with and 



controlled by the cells in 

 the cerebral hemisphere of 

 the other side. Although 

 there are a few exceptions 

 to this arrangement, this 

 is, in the main, the rela- 

 tion of the spinal cord to 

 the rest of the body. 



THE PERIPHERAL NER- 

 VOUS SYSTEM 



The nerves over which 

 messages are brought to 

 the spinal cord or the 

 brain and those over 

 which messages are sent 

 out compose the periph- 

 eral nervous system. 

 These nerves are classed 

 in two groups: (1) the 

 cranial nerves which go to 



or leave the brain directly without entering the cord; (2) 

 the spinal nerves which enter and leave the cord. 

 The Cranial Nerves. The cranial nerves are twelve in 



^ Vagus 

 to Heart &Lttnejs 



FIG. 157. DIAGRAM 



Showing the distribution of the different cranial 

 nerves. The numbers indicate the number 

 of each nerve, and the arrows show whether 

 each is afferent or efferent. 



