206 



TWENTIETH LECTURE. 



Klebs and others) had met in this tissue formation with 

 plexuses or net- works of pale, fine nerve fibres with nuclei in 

 the nodal points. This net-work was regarded as terminal. 

 Others have, however, proceeded further, whether correctly 

 we certainly doubt. 



Arnold, who has investigated these things most accurately, 

 gives us the following information concerning them : 



The nerve trunks of the smooth muscular tissue (Fig 180) 

 consist in part of medullated, in part of non-medullated fi- 

 bres. The latter diminish 

 into nucleated filaments mea- 

 suring 0.0018 to 0.0023 mm. 

 Even externally in the con- 

 nective tissue surrounding 

 the muscular substance, there 

 occurs a wide-meshed plexus, 

 having ganglion cells in 

 places, Arnold's so - called 

 basis plexus. From the lat- 

 ter pass nucleated fibres, 

 which become pale, longitu- 

 dinally striated, nucleated fil- 

 aments, 0.0041 to 0.005 mm - 

 in diameter. The latter grad- 

 ually diminish to 0.0018 to 

 0.0023 mm. 



From these — though pale 

 and, therefore, non-medullated fibres also enter it from the 

 basis plexus — there is formed a second and likewise tolerably 

 wide-meshed reticulum, which also has nuclei at the nodal 

 points. This is Arnold's intermediate plexus. It is either 

 closely applied to the smooth muscles, or lies in the connec- 

 tive tissue between the several layers of the first-mentioned 

 tissue. 



From this second plexus pass off fine fibres, which are at 

 first still nucleated. They rapidly become finer, and pass be- 

 tween the contractile fibre cells. Finally, after repeated divi- 



Fig. 180. — The termination of the nerves in the 

 smooth muscles of a frog's artery. 



