TERMIXATION OF NERVES IN MUSCLE. 153 



capsule, and passes some way on its wall, sometimes in a spiral direc- 

 tion (Bowman). 



Tliere is considerable difference of oj^inion as to the condition of the nerve- 

 iibre in the Pacinian body. KoUikcr thinks that it retains its ijrimitive sheath, 

 and is not wholly dejirived of its medulla ; and that the smrounding: core is com- 

 I^osed of a nearly homogeneous connective tissue, in wliich he has seen faintly 

 marked nuclei and faint longitudinal striation.* Engelmann, on the other hand, 

 considers the core to be an expansion of the medullary sheath of the nerve, and 

 ascribes the appearances noticed by KoUiker to changes occurring in the originally 

 homogeneoiis medulla, as in the case of a white nerve-fibre. The pale fibre 

 within he considers to be simply the axis-cylinder. The core and pale fibre of 

 the end-bulbs he regards in precisely the same way, and thinks it not improbable 

 that the touch-cor^iuscles will be found to conform. He looks upon the simple 

 capsule of the end-bulb as a development of the juimitive nerve-sheath, to which, 

 in the Pacinian bodies, is superadded a series of concentric coats of connective 

 tissue. Engelmann, besides adducing other arguments, refers especially to the 

 structui-e of the Pacinian bodies of birds, as aifording material evidence in support 

 of his view. 



To us the core of the Pacinian corpuscle seems most nearly to corresijond 

 in its anatomical relations with the j^rotoplasmic layer which Ran\'ier has 

 described as existing, especially in young nerves, between the primitive sheath 

 and the medullary sheath of the nerve-fibre, in which case the innennost 

 capsule of the Pacinian, with its nuclei, would answer to the nucleated sheath 

 of Schwann or primitive sheath of the ner^-e. For in the first place there 

 can be little doubt that the capsules are expansions of the lamella; of the 

 nemilemma, with which they agree essentially in stnictm-e. In the second 

 l^lace, we have never been able to observe any stnictui-e resembling a primitive 

 sheath immediately sm-rounding the nei-^'C as it passes through the core. We 

 have, however, more than once observed a nerve-fibre pass through one Pacinian 

 to end in another, without at all being divested of its medullary sheath as it 

 traversed the core of the first. In such cases, as well as in others, in which the 

 medullary sheath is retained for a certain distance within the core, it is easy to 

 see, in oj^position to Eng'elmann"s view, that the substance composing the core 

 jjresents a marked contrast to the medullary sheath. Neither is it, like the latter, 

 deeply coloiu-ed by osmic acid (Michelson) or by chloride of gold, but. on the 

 contrary, is only moderately stained by these re-agents. 



Nothing jiositive is known concerning the special pui-pose in the animal 

 economy which these curious appendages of the nerves are destined to fulfil. In 

 an anatomical sense a Pacinian bodj- might be viewed as a more complex develop- 

 ment of an end-bulb, from which it differs chiefly in the multiplied layers of the 

 capsule. W. Krause endeavours to show that the series of concentric capsules 

 with interposed fhiid is an aiTangement for converting the effect of mechanical 

 traction into fluid pressvire upon the neixe, so that tension and traction of the 

 tissue in which the corpuscle is placed, may be felt and appreciated as ordinary 

 pressiu'e. Theii' presence in the mesentery of the cat seems, at first sight, 

 against their importance as sentient organs, but it turns out upon trial, that the 

 part m question is remarkably sensitive. 



Other special modes of termination of sensor}^ nerves as, for instance, 

 in the organs of special sense, will be most conveniently considered in 

 the description of the organs to which they belong. 



Termination of nerves in muscle : — A. In plain or unstriped 

 muscle. — Beale, and, after him, Kiebs and others, have described the 

 nerves proceeding to the involuntary fibres as finally distributed in 

 networks of nou-meduUated fibres, with nuclei at intervals. The net- 

 W'Orks are at first coarse, and from them proceed finer bundles and 



* See also Axel Key aud Retzius, loc . cit. 



