MOVEMENTS OF VOLUNTARY MUSCLE. 
491 
the shortening of the fasciculus. I have not seen this in contracted fasciculi that 
have not been wetted, and, therefore, conclude the sheath to be endowed with the re- 
quisite elasticity for accommodating it to the varying form of its contents. But 
where bullse are developed, the folds thus occasioned are strongly marked, and have 
very probably been not unfrequently mistaken for transverse rugae upon the fasci- 
culus. The fibrillae, however, are entirely independent of them, as may be seen in 
specimens taken from the Newt (fig. 76-) and Mouse (fig. 80.). In those Birds that 
have been examined, the irritability has so speedily ceased, that no contraction has 
been observed. 
It is almost unnecessary to remark how completely the variety before noticed in 
the proximity of the striae in all animals in contiguous and even the same fasciculi, 
is illustrated and explained by the foregoing facts. 
Such are the principal phenomena observed during that form of contraction which 
I conceive to be analogous to the rigor mortis but it is undoubtedly necessary to 
bear in mind, that the fasciculi in which they occur are in a condition very different 
from those acting in the living body under the influence of volition. It is not by 
any means intended to be implied, that the healthy movements of muscle are in every 
respect such as have been now described ; but it seems highly probable, that in kind, 
at least, they are identical with them. Perhaps, therefore, the mechanism of volun- 
tary motion may receive some elucidation from this phenomenon of lingering vitality. 
A muscle, if cut whilst irritability remains, retracts to a greater or less extent, as is 
seen every day in amputations ; this is by virtue of a tendency, always existing, 
towards approximation of the discs, for if a piece so cut be immediately examined, 
the strirn are seen regular in form, and the fasciculi without rugae. The contraction 
just now described is a subsequent change ; and in it a still further approximation of 
the striae is observed, often so great as to diminish the whole length by more than a 
half, which is more than occurs in living muscle, even during extreme action. Now 
the consequence of this is not always the production of even any disturbance of the 
straight direction of the fasciculus, though small rugae are frequently formed. From 
this it is evident, that the discs have a very extensive range of motion, quite suffi- 
cient to effect, without other mechanism, the ordinary movements of volition. 
Now with regard to the existence of the rugae and zigzags in the living body, there 
* It will probably be no longer doubted, that this interesting and much-canvassed phenomenon is to be 
ascribed to the muscles ; and it need hardly be said how close a bearing the observations above detailed will 
have on the explanation of its physical mechanism. For impartial evidence of the present unsettled state of 
the question, consult Muller’s Physiology, Baly’s Translation, p. 890 et seq. 
It is also evident that these observations prove the property of contractility to be inherent in the very struc- 
ture of muscle, and to be capable of being called into action without the immediate instrumentality of nerves ; 
for the fasciculi submitted to examination, after being entirely isolated from every surrounding structure, and 
then remaining some time in a state of rest, have frequently exhibited the contractions described, on the ad- 
dition of water, which seems to act as a stimulus to them, or by the accidental pressure on some point of their 
surface of any extraneous fragment of dirt that might happen to be present in the field of the microscope. 
3 r 2 
