STRUCTURE OF THE PACINIAN CORPUSCLES. 139 
tunics, as Key and Retzius propose, would be productive of 
endless confusion, the term having been so long used in a 
different sense. 
By far the readiest mode of demonstrating the fibrous 
structure of the coats of the Pacinian is to immerse the latter 
in dilute solution of chromic acid (4 per cent.) for some days, 
and then either to make thin sections of the corpuscle with 
a razor, or carefully to break it up with needles upon a 
glass slide. If the latter method be employed it will be 
found that the tunics of which the capsular envelope is 
composed very readily tear in a direction transverse to the 
axis of the corpuscle, and small shreds are obtainable which 
exhibit the general structure of the tunics and the arrange- 
ment of the fibres within them in the clearest possible man- 
ner. ‘This is shown in surface view in fig. 6, Plate 1X, and 
in profile in fig. 5; the details of the structure will be best 
understood by referring to the description of the Plates. 
Continuity of the Slructures composing the Entering Nerve 
with those of the Corpuscie. 
The entering nerve of the Pacinian corpuscle consists 
usually of a single medullated fibre enclosed in a prolonga- 
tion of the neurilemma of the nerve-trunk from which it 
springs.! 
Enumerating the structures which compose the nerve-fibre 
and its special sheath from within out, there is, first, the 
axis-cylinder occupying the centre of the fibre; around this 
the medullary sheath or white substance of the nerve; im- 
mediately external to this a delicate layer of protoplasm with 
clear oval nuclei imbedded in it at definite intervals (the 
protoplasm is more abundant in the neighbourhood of the 
nuclei, and the layer is, moreover, much better marked in 
young nerves); this protoplasmic layer is enclosed by the 
' By the term xeuwrilemma has long been described and is commonly 
understood the special sheath, now ascertained to possess a laminated 
structure, which envelopes each funiculus or bundle of nerve-fibres, and a 
prolongation of which may often be traced accompanying even single fibres, 
as, for instance, in the case of those passing to the Pacinian corpuscles. 
Moreover, Ranvier, to whom we owe much of what is known concerning the 
structure of the funicular sheath, retains the use of the term. Owing, 
however, to its having been applied somewhat indiscriminately, and occa- 
sionally used to indicate the sheath of Schwann or primitive sheath of the 
nerve-fibre, many histologists altogether deprecate the employment of the 
term, and substitute for it that of perinewrium. 1 shall in this article 
continue to employ the term ‘neurilemma,”’ since it is in common use in 
this country, it being, however, clearly understood that the laminated 
funicular sheath alone of the nerve is thereby meant. 
VOL. XV.—NEW SER. K 
