MOVEMENTS OF VOLUNTARY MUSCLE. 
487 
pearances of two fasciculi out of many similar ones, taken from the leg of a common 
Blue Bottle Fly ( Musca vomitoria). These are detached from one another, and each 
has united to it the small set of tendinous fibrillse (here stiff, and somewhat horny, 
but divisible into exceedingly minute threads,) serving to prolong it to its fixed at- 
tachment. In these beautifully delicate parts, the following circumstances may be 
observed. 1st. The tendon expands to fix itself to the extremity of the fasciculus, 
and there abruptly terminates, the line of union being definitely notable. 2nd. The 
extremity of the fasciculus being with certainty apparent, has precisely the same ap- 
pearance as its other parts, presenting a perfect terminal disc, and the sarcolemma 
attached to its border. The corpuscles also advance as far as the extremity. 
On the Mechanism of the Movement of Voluntary Muscle . 
Nothing certain is yet known concerning the more minute changes which the pri- 
mitive fasciculi undergo during a state of contraction. The theory of Prevost and 
Dumas, though still finding a place in the best physiological works, seems to be falling 
every day into more general discredit. Many who have endeavoured to inspect the 
phenomenon on which it was based, have failed in convincing themselves that it is 
the true condition of contraction ; and others, though noticing the fact of the zigzag 
flexure of the fasciculi, have not confirmed the account given of the correspondence 
of the angles to the transit of nerves. Professor Owen has been led to doubt it “from 
observing the contraction of the muscular fibres in small filarise (such as commonly 
infest the abdominal cavity of the Cod), and more especially from observing the con- 
traction of the retractor muscles of a species of Vesicularia. “Each separate fibre 
of the retractor muscle,” he says, “ is seen with great distinctness, and is characterized 
by a single knot or swelling in the middle. In the act of retracting the tentacles, the 
fibres become shorter and thicker, especially at the central knot, but do not fall out 
of the straight line*.” I am ignorant whether these be fasciculi having transverse 
strise. If not, the bearing of the observation on the contraction of striated muscle is 
less direct and important. The same acute observer afterwards explains, that the 
zigzag folding of the fibres is characteristic of their state of relaxation, when not 
stretched by antagonist muscles. Dr. Allen Thomson also, on repeating the experi- 
ment of Hales and Prevost on the Frog, “ observed single fibres continuing in con- 
traction, and being simply shortened, and not falling into zigzag plicae : and he was 
led to suspect, from this and other circumstances, that the zigzag arrangement was 
not produced until after the act of contraction had ceasedf.” M. Lauth, who seems 
to have investigated this subject most carefully, states that a fasciculus may shorten 
with or without gigzag inflexions ; but he supposes that at all times the fasciculus 
presents in its whole extent transverse rugte, which may probably, he says, be due 
to the contraction of the primitive fibrillae^:. Muller says, that contraction by the 
* Hunter’s Works, Palmer’s Edition, vol. iv.. Note, p. 261-2. f Ibid. 
+ L’lnstitut, No. 73, quoted by Muller, Baly’s Translation, p. 8S8. 
