! 



282 THE HUMAN BODY. 



such a word, i^ ..-epresented by the nervous system, which 

 is in communication with all the other organs, is influenced 

 by the condition and the needs of every part at each mo- 

 ment, and guides the activity of all the others accordingly. 

 Part of this control is exercised consciously and with the 

 co-operation of the "will," but much more is carried on by 

 the nervous system without our knowing anything about it. 

 Nerve-Trunks and Nerve-Centres. In dissecting the 

 body numerous white cords are found which at first sight 

 might be taken for tendons. That they are something else 

 soon becomes clear, since a great many of them have no 

 connection with muscles, and those which have, usually 

 enter near the middle of the belly of the muscle, instead of 

 being fixed to its ends as most tendons are. These cords 

 are nerve-trunks : followed from the middle line of the 

 body each (Fig. 79) will be found to break up into finer 

 and finer branches, until the subdivisions become too small 

 to be followed without the aid of a microscope. Traced 

 towards the middle of the body the trunk will, in most 

 cases, be found to increase by the union of others with it, 

 and ultimately to join a much larger mass of different 

 structure, from which other similar trunks spring. This 

 mass is nerve-centre. The end of a nerve attached to the 

 centre is, naturally, its central, and the other its distal or 

 peripheral end. 



What is it in the body which represents the master builder? 

 What are the relations between the nervous system and the other 

 organs of the body ? Is the control of the nervous system always con- 



ly exercised? 



How n.ay we recognize that certain white cords found on dissect- 



T the be ly -in not tendons? What are they? What is found when 



iced towards the outer parts of the body? What 



a traced m the opposite direction? What is a nerve-centre? 



.1 by lie peripheral end of a nerve? 



