NERVE TRUNKS. 115 



cylinder is preserved ("Monthly Microscopical Journal," 

 1872). 



"What appears as the single core or 'axis cylinder 1 of a 

 nerve fibre in the nerve trunk is formed by the coalescence of 

 very numerous fine fibres, each coming from a different central 

 nerve cell. In following a single dark-bordered, or other nerve, 

 towards centre or periphery, we find that it divides and sub- 

 divides into a great number of fibres, which pursue different 

 and often opposite directions, one passing towards the centre, 

 and the other to the periphery. And these are implanted in 

 different parts of the nerve centre or peripheral organ at con- 

 siderable distances from one another" ("Biopl.,"p. 177). 



The effect of the frequent crossing and interlacing and 

 change of course of the nerve fibres, Dr. Beale pointed out, is 

 to prevent the complete paralysis of either motion or sensation 

 of any part by injuries of a moderate number of nerve fibres. 



The so-called pale fibres of the sympathetic do not differ essen- 

 tially from the dark bordered nerves. There is simply no 

 medullary sheath, where the distance between the nerve 

 centre and the peripheral distribution of the nerve is not very 

 great. " Where, however, the ganglia, or peripheral organs are 

 connected with nerve centres at a considerable distance off, a 

 number of fibres having this investment are found ; so that 

 amongst the sympathetic nerve fibres we find dark bordered 

 nerve fibres. In the bladder of the frog I have observed that 

 when the distance between the ganglia and the peripheral dis- 

 tribution of the nerve fibres is considerable, the fibres have the 

 dark bordered character, while on the other hand, if the peri- 

 pheral distribution is near the ganglion, the ultimate nerve 

 fibres are connected with the latter by pale fibres only" ("Biopl./' 

 176), Dr. Beale has also demonstrated the existence of very 

 fine fibres running close to the dark bordered ; these fibres in 

 fact result from division of the dark bordered fibres, and are, 

 in fact, a continuation of them near the point of their distri- 

 bution. 



On the Nerve Centres. While in the lowest animals there is 

 no obvious distinction between peripheral and central parts of 



82 



