230 THE NERVOUS SYSTEM 



medullary substance and divide to form arborization which 

 are flattened into the form of a leaf. 



(e) The corpuscles of Golgi are situated at the point of 

 union of tendons with muscles, and are believed by some to 

 have to do with the muscular sense. They are flattened fusi- 

 form bodies composed of granular substance enclosed in 

 layers of hyaline membrane and containing nervous fibrillae. 



Properties and Classification of Nerve Fibers. Nerve 

 fibers are for the purpose of conveying messages either peri- 

 pherally or centrally. They may be stimulated to action by 

 anything capable of suddenly increasing their irritability. In 

 any case the effect of the stimulus, whether normal or ab- 

 normal, is manifested at the peripheral distribution of the 

 stimulated fiber. So far as most external manifestations are 

 concerned, nerves may be classified as motor and sensory. 

 That is to say, stimulation, for instance, of a cerebro-spinal 

 nerve (except those of special sense) is followed, under or- 

 dinary conditions, by one of two results there is either 

 pain or contraction of a muscle to which the nerve is dis- 

 tributed. This is a typical illustration of the action of motor 

 and sensory fibers, and the manifestation of nerve action, 

 whether it consists in pain or motion, is a result only of the 

 conduction of an impression of an impulse to the center or 

 the periphery. It is to be noted that the result of thus stim- 

 ulating a nerve fiber is manifested at one extremity only of 

 that fiber, and always at the same extremity. 



However, since there are nerve fibers the stimulation of 

 which is not followed by pain or motion, the division into 

 sensory and motor fibers is not comprehensive enough to in- 

 clude all the fibers in the body. But since, as above stated, 

 the only office of fibers is to conduct, and since they always 

 conduct in a direction either tozvard or away from the cen- 

 ter, all nerves may be classified as either centripetal or cen- 

 trifugal. A corresponding division is into afferent and 

 efferent. It will be seen that all motor fibers are centrifu- 

 gal or efferent, but not all centrifugal or efferent fibers are 



