324 MANUAL OF HISTOLOGY. 



eminence is not the true terminal structure. The nerve fibre, he says, becomes 

 forked (amon the arthropods) at the summit of the eminence, giving off two fibrils. 

 These latter then travel the substance of the terminal plate, and breaking up into 

 numerous filaments, end in the fleshy mass of the muscular element. 6. According 

 to Scale, there is situated on the exterior of the sarkolemma a very fine nucleated 

 network'of nervous elements, to which formation this English investigator ascribes 

 just as little terminal significance as elsewhere in the body, in that the nerves are 

 only spread out peripherally in loops. A similar view of the subject had been pre- 

 viously taken by Schafhausen. The statements of such a man as eale, however, 

 and the peculiar methods of investigation made use of by him, deserve more con- 

 sideration than has as yet been given them. Koellikcr's views, as regards the termina- 

 tion externally upon the sarkolemma, correspond with those of Beale. On the other 

 hand, he only recognises pale terminal fibres in the frog, which he regards as con- 

 tinuations of the axis cylinder and primitive sheath, and which probably end, as a 

 rule, naked. He encountered, however, some isolated cases, which seemed to indicate 

 a termination in a very fine dense network. Margos views, on the other hand, are 

 completely different. According to him, the nerve pierces the sarkolemma, sinks 

 into the fleshy matter, and is in communication here with a peculiar terminal 

 apparatus. The latter he looks upon as formed of the greater part of the muscle 

 nuclei and the network of the so-called interstitial granular threads ( 166). 



183. 



Turning now to unstriped muscular tissue, we find it far more difficult 

 to recognise in it the final distribution of the nerve fibres than in the tissue 

 we have just been considering. Division occurs here also, as has been seen, 

 for instance, in the stomach of the frog and rabbit by Ecker ; in the heart 

 of amphibia and nerves supplying the uterus of rodentia by Kilian. 



In the mesentery of the frog (fig. 312), moderately treated with acetic 

 acid, we may observe in the narrow medullated nerve fibres enclosed in 

 a thickened envelope several repeated dichotomous divisions, until at 

 last the branches penetrate the walls of the part and are removed from 

 further observation. These fibres are enclosed, as was before indicated, 

 in a thick nucleated envelope. 



But what becomes of these nervous elements on arrival in the unstriped 

 muscular tissue ? 



This is a question which for a long time remained without any satis- 

 factory answer. It is true that years ago plexuses or networks of pale 

 delicate filaments had been met with, with nuclear structures at the 

 expanded nodal points, and that this network was held by many to be a 

 terminal structure, which view seemed strengthened by the fact of the 

 occurrence of a similar nervous end-formation in the electric organs of the 

 ray. 



But not long ago an important discovery apparently was made by 

 Frankenhduser, subsequently confirmed by Lindgren, and more recently 

 still through the most comprehensive researches by Arnold. This was 

 that the nerve fibres of smooth muscle penetrate to the nucleus of the 

 contractile cell in the form of a fine terminal filament, the primitive 

 fibrilla, and end probably in the nucleolus. 



From Arnold's experiences it would appear that the nervous twigs sup- 

 plying unstriped muscle consist partly of medullated and partly of non- 

 medullated fibres, in varying proportion. We encounter the latter as 

 fine or broad threads, measuring in diameter 0'0018-0'002 mm., and 

 showing at intervals small nuclei. Externally, in the connective-tissue 

 covering the muscle, these nerves are arranged in the form of a wide- 

 meshed network, in which, as Scale has pointed ou*-, ganglion cells are 

 to be found at certain points in the muscles of the vascular system. To 

 this the name "ground plexus" lias been given (1). 



