MOVEMENTS OF VOLUNTARY MUSCLE. 
489 
and sarcolemma, giving rise to the appearances of bailee already described. It often 
happens, but not necessarily, that besides the approximation of the strise, the con- 
tracted portion exhibits inflexions at distances, sometimes nearly regular, but generally 
not so, and including from five to thirty, or forty striae. These inflexions are very 
slight, and engage either a part or the whole of the fasciculus. They do not occur 
even when most regular, at special and determinate situations, but may often be seen 
to alter their position as contraction proceeds, probably in consequence of its irregu- 
larity. These inflexions or rugae, however, are not peculiar to the contracted part, 
but are seen not unfrequently in fasciculi, which present no contractile movements, 
and no unusual proximity of the transverse striae. The contracted part of the fasci- 
culus may be frequently recognized merely by its greater opacity, and its more evi- 
dent, longitudinal striae*. 
It happens, as might be expected, that these several circumstances are seen under 
considerable varieties in different animals and modes of observation, but in the main 
they are very constant and easy of demonstration. In Mammalia, as the Mouse; in 
several Reptiles, as the Frog, Newt, Adder ; in Fish, as the Eel, Skate ; and in Crus- 
tacea, as the Crab and Lobster; and in Insects, they have been repeatedly witnessed 
by many gentlemen to whom I have shown them (see Plate XIX.). In the three latter 
classes, however, they are best seen, and best of all in the Crab and Lobster, for the 
tardiness with which the irritability of these animals departs, prolongs the period of 
observation, and renders the stages of the phenomenon more distinguishable from one 
another. The contraction, besides occurring at the ends of the fasciculi, often begins 
independently at one or more intermediate points, and can here be observed under 
peculiarly favourable circumstances, for the muscle is very transparent, though the 
fasciculi are of extraordinary dimensions. 
The first appearance is a spot more opake than the rest, caused by the approxima- 
tion of a portion of a few of the discs towards each other; that is, by the shortening 
and gathering together of a few segments of a limited number of fibrillse. By altering 
the focus, the phenomenon may be ascertained to extend as much in depth as in 
breadth, so that the contracted portion may be compared to a solid ball, lying in the 
midst of uncontracted and flaccid parts. If this ball beat the surface, the almost in- 
variable concomitant is a collection of expressed water in bullse between the sarco- 
lemma and fibrillse. The contractile force seems to be exerted solely in the direction 
of the length of the fibrillse, for in this direction only are the strise beyond the spot 
distorted. The distortion consists of an extreme stretching and widening of them 
and their interspaces, which is greatest close to the ball, and gradually ceases at a 
distance of thirty, forty, or more strise: thus the fibrillse not implicated in the con- 
tracted ball are undisturbed, while those so implicated have their segments drawn 
* Owing to the polygonal, and sometimes flattened form of the fasciculi, they may present, if twisted, an 
appearance of unequal thickness at different points of their length, without there being, in fact, any contrac- 
tion, or approximation of the transverse striae. 
3 R 
MDCCCXL. 
