MOVEMENTS OF VOLUNTARY MUSCLE. 
479 
light striae, between which the real margin of the fibrillse recedes from it, with an 
intervening fluid. Now in this specimen the interior of the fasciculus is in focus ; a 
central row of corpuscles is there seen, and the view of the margin thus represented 
is, in fact, such as would be obtained by a horizontal section. This fasciculus is thus 
proved to present on its surface a series of transverse grooves, to which the sheath 
does not adhere, and in which a fluid is collected. It seems doubtful whether the 
attachment of the sarcolemma to the prominence of the successive discs be so com- 
plete as to isolate the intervening grooves from one another. 
Another evidence of this adhesion is the following : when the hernise are formed 
as above mentioned, it is of course so far destroyed. Now, the intumescence is oc- 
casionally so great, that the sarcolemma is rent extensively on all sides, and fragments 
of it only remain, not embracing the whole fasciculus. Wherever the fibrillse have 
detached themselves from the sheath they bulge freely, but where they continue to 
adhere to its remnants, they are confined and constricted, and the strise cannot 
expand (fig. 46 .). This adhesion will afford an explanation of an appearance that for 
some time puzzled me. It is described by Mr. Skey in the following terms : “ A fibre 
(primitive fasciculus) is frequently elongated to a point, up to the extreme external 
surface of which the circular strise are apparent. If the fibre be a solid cylinder,” 
he then asks, “ What becomes of the central substance ? for it is evidently the external 
surface that is so attenuated, indicated by the presence of the circular strise*.” This 
kind of fracture, which in Mammalia not unfrequently occurs during the manipula- 
tion, is occasioned, I suppose, by traction on the opposite ends of the fasciculus. The 
superficial fibrillse do not break so soon as the central ones, because they are supported 
by the sarcolemma , which has been already shown to be the more extensible structure : 
this stretches them, and when at length they give way, they are much attenuated, 
fall together over those in the centre, and come to a rude point. From the same 
cause the extremity of a broken fasciculus sometimes may present an appearance of 
a tube. What much corroborates this explanation is, that in such cases the terminal 
strise are always much widened and distorted. 
If the fasciculi be placed in water, some of this fluid is absorbed by them, and they 
undergo an increase in bulk. This may explain why so many authors have differed 
from the accurateLEEUwENHOEK and Prochaska, and asserted them to be of a cylindri- 
cal form, for when thus swollen they lose much of that angular shape, which is so 
convenient and necessary for close package in the natural condition. I allude to this 
fact, however, for the purpose of introducing a description of one of the most instruc- 
tive phenomena connected with this investigation. It regards muscle, not in a passive, 
but an active state; and besides exhibiting the condition of the fibrillse during con- 
traction, which for the present I omit noticing, furnishes a further proof of those 
qualities and relations of the sarcolemma that have been ascribed to it above. It 
occurs in fasciculi just taken from the animal, either still living or a moment dead, 
* Philosophical Transactions, 1837, p. 378. 
