ELECTROMOTIVE ACTION IN NERVE 



reach the contractile substance ; the medullary sheath, as a rule, 

 terminates shortly before the definite ending. Stress must be 

 laid upon the much-disputed fact of the passage of the axis- 

 cylinder, since, admitting certain premises as to the nature of the 

 propagation of a stimulus, the sarcolemma would offer no absolute 

 hindrance. The axis-cylinder seldom remains entire, but exhibits 

 a more or less copious arborisation (Ktihne's terminal arborisation), 

 " hypolemmal " in situation, and occurring according to two types, 

 (a) in amphibia (Fig. 222), (b) in reptiles, birds, and mammals. 

 The former presents tolerably straight, rounded, or flattened 

 terminal branches, running parallel with the axis of the muscular 

 fibre ; these extend widely for some little distance close under 



FIG. 222. Arborisation from frog's gastrocnemius. (Kiihne.) 



the sarcolemma, and always end distinctly in a blunt point. 

 Here and there they bear long, oval nuclei, which Ktihne termed 

 " end-buds." In contrast with these " branches " are the " plates " 

 of other vertebrates, where the rami take a bending and intricate 

 course, or form laminal, lobed expansions within a small circular 

 or oval " field of innervation," that rarely comprises the whole 

 muscle-fibre (Figs. 223-225). It is characteristic of these "end- 

 plates " that they nearly always present a more or less conspicuous 

 accumulation of finely -granulated substance set with nuclei 

 (sarcoplasm), within which are embedded the ramifications of the 

 axis-cylinder (Klihne's "end-plate," Fig. 224). In the branched 

 form this " granulosa " is seldom perceptible, while in the plates it 

 is frequently well-developed and appears in profile as a projecting 

 expansion, corresponding with Doyere's expansion in insect-muscle 

 (Fig. 225). 



