THE SPINAL CORD 525 



serves to arouse in the individual a consciousness of the existence of an 

 external world, by virtue of the impressions which it makes on his sense 

 organs, and consequently to enable him to adjust himself to his environment. 



By virtue of the anatomic and physiologic association, a stimulus, if of 

 sufficient intensity, applied to one organ or tissue will call forth activity 

 in one or more organs near or remote from the part stimulated. This 

 I coordination of action is accomplished mainly by the spinal cord and the 

 [medulla oblongata. Alljactions which take place in response to a periph- 

 eral stimulus and independently of volition are termed reflex actions. The 

 reflex activities connected with digestion, the circulation of the blood,^with 

 respiration, excretion, etc., are illustrations of the coordinating capabilities 

 of the nerve-centers located in these portions of the central nerve system. 



By virtue of the physiologic activities of the encephalon and more 

 particularly of the cerebrum and of the relation existing between it and the 

 sense organs of the body, consciousness of the existence of an external 

 world and the individual's relation to it is developed. Experimental and 

 clinic investigations show that of the parts of the encephalon, the cerebrum 

 is the chief, though not perhaps the sole organ of the mind and that its 

 functions are for the most part mental. 



The function of a part at least of the peripheral nerve system is to afford 

 a means of communication between the central organs of the nerve system 

 and the remaining structures of the body. 



The nerve-trunks constituting this part of the nerve system may I 

 divided into two groups, as follows: 



1 The first group comprises nerves in connection with the special sense 



organs, e.g., skin, eye, ear, nose, tongue, as well as nerves in connection 

 with the general or organic sense-organs, e.g., mucous membranes, 

 viscera, etc., which are connected primarily with nerve-cells in the spinal 

 cord and medulla oblongata, and secondarily with nerve^cells in 1( 

 ized areas of the cerebral cortex. . . 



2 The second group comprises nerves which terminate mainly in the 



muscle apparatus and which constitute the continuation of nei 

 which have their origin in nerve-cells of localized areas of the c 



ThTfirst group of nerves, the afferent, especially those connected with 

 the special sense-organs, are excited to activity ^PfJ^^f^ 

 peripheral terminations by agencies m the external world The nerve 

 impulses thus generated are transmitted m part only as far 

 cord and medulla oblongata while the remainder ascend ; e ' c ^ '" 

 localized areas of the cerebral cortex where they evoke sensations. 



- 



in their related n.rve-ce Is .te 1 '">>" v 



c * ffi 



become physical expressions of mental states, and if direct 



