CHAPTER XII. 



ANATOMY OF THE NERVOUS SYSTEM. 



K erve-Tnmks.' In dissecting the Human Body numer- 

 ous white cords are found which at first sight might be 

 taken for tendons. That they are something else however 

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

 connection with muscles at all, and those which have usually 

 enter somewhere into the belly of the muscle, instead of be- 

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

 nerve-trunks: followed in one direction each (Fig. 62) 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 the other way 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, and from which other trunks also 

 spring. This mass is a nerve-centre. That end of a nerve 

 attached to the centre is naturally its central, and the other 

 its distal or peripheral end. Nerve-centres, then, give origin 

 to nerve-trunks; these latter radiate all over the Body, 

 usually branching and becoming smaller and smaller as 

 they proceed from the centre; they finally become very 

 small, and how they ultimately end is not in all cases cer- 

 tain, but it is known that some have sense-organs at their 

 terminations and others muscular fibres. The general ar- 

 rangement of the larger nerve-trunks of the Body is shown 

 in Fig. 62. Physically a nerve is not so tough or strong as 

 a tendon of the same size; it may readily be split up into- 

 longitudinal strands, each of which consists of a number 

 of microscopic threads, the nerve-fibres, bound together by 

 connective tissue. 



