120 END-PLATES. [BOOK i. 



parts, the ramified axis cylinder, and the granular nucleated sole, 

 the two apparently, though in juxtaposition, not being continuous. 

 According to some observers the sole is continuous with and indeed 

 is a specialized part of that substance pervading the whole muscu- 

 lar fibre which we spoke of as interh'brillar substance. We 

 cannot enter here into a discussion of the probable meaning 

 and use of these structures or how they effect what seems 

 obviously their function, the transformation of the changes 

 constituting a nervous impulse into the changes, .which running 

 along the muscle fibre in the latent period as forerunners of the 

 changes entailing actual contraction, may be spoken of as con- 

 stituting a muscle impulse. It is of interest to observe that 

 certain analogies may be drawn between an end plate and the 

 histological elements of the so-called electrical organs of certain 

 animals. The element of the electric organ of the torpedo, for 

 instance, may be regarded as a muscle fibre in which the nerve 

 ending has become highly developed, while the muscle substance 

 has been arrested in its development and has not become striated. 



In amphibia (e.g. in frogs) the ending of a nerve fibre in a 

 muscle fibre is somewhat different. A nerve fibre about to end in 

 a muscle fibre divides into a brush of several nerve fibres, each of 

 which, losing its sheath of Henle and sarcolemma, enters the same 

 muscle fibre, and then losing its medulla runs longitudinally along 

 the fibre for some distance, it and its branches dividing several 

 times in a characteristically forked manner, and bearing at 

 intervals oval nuclei. In other animals forms of nerve ending 

 are met with more or less intermediate between that seen in the 

 mammal and that seen in the frog. 



70. Besides the medullated nerve fibres described in 68, 

 there are in most nerves going to muscles a few and in some 

 nerves, going to other parts, a large number of nerve fibres which 

 do not possess a medulla, and hence are called non-medullated 

 fibres ; these are especially abundant in the so-called sympathetic 

 nerves. 



A non-medullated fibre which, like a medullated fibre, may 

 have any diameter from 2/j, or less to 20/i or more, is practically a 

 naked axis cylinder, not covered with medulla, but bearing on its 

 outside at intervals oval nuclei disposed longitudinally. These 

 nuclei appear wholly analogous to the nuclei of the neurilemma of 

 a medullated fibre, and probably belong to a sheath enclosing each 

 fibre, though it is not easy to demonstrate the independent exist- 

 ence of such a sheath in the case of most non-medullated fibres. 

 In the similar fibres constituting the olfactory nerve a sheath is 

 quite conspicuous. Unlike the medullated fibres these non-medul- 

 lated divide and also join freely ; like them each may be regarded 

 as a process of a nerve cell. 



Of such non-medullated fibres a scanty number are found in 

 nerves going to muscles scattered among the medullated fibres 



