492 
MR. BOWMAN ON THE MINUTE STRUCTURE AND 
is a difficulty in comprehending 1 how they can be caused by the approximation of the 
discs : and to suppose them produced by a different principle, seems at variance with 
our experience of the simplicity displayed in all the operations of nature. The only 
way in which it would appear possible for the rugae to be formed through the instru- 
mentality of the discs, is by assuming a partial contraction on alternate sides of the 
fasciculus, the concavity of the bend having the closest set striae; but a force thus 
expended must act at immense disadvantage, and it will not explain the zigzags, which 
often include many smaller rugae within them*. Independently of this objection, 
these flexuosities have been shown by the observations of Professor Owen, to be cha- 
racteristic, in filariae, of the relaxed state of the fasciculi, under the circumstances 
which bring their two attached extremities nearer each other •f'. Moreover, in ex- 
amining the abdominal muscles of the Frog, I have found that, after their irritability 
has ceased, the zigzag plicae may be very readily produced at pleasure by approxi- 
mating mechanically the extremities of the fasciculi ; and it cannot surely be thought 
extraordinary, that under such circumstances the zigzags should often be of nearly 
uniform size, or that the passage of vessels or nerves among the fasciculi should have 
the effect of determining the flexures to take place at this or that particular point. 
I have likewise observed the same thing in various muscles examined under the 
microscope. Hence it is highly probable, that flexures are always the natural posi- 
tion into which fasciculi are thrown, if, on elongation following contraction, they are 
not at once stretched by antagonist muscles. 
But how is it that, in living muscles undergoing contraction, zigzag plicae have 
been seen to occur? The independent power of action of the individual fasciculi has 
been already shown; and what is more probable than that, in a contracting muscle, 
these are not all acting at once, but that some contract while others are relaxed ? I 
laid bare the muscle of a living Pvabbit, and took hold of a portion of it with a pair 
of forceps in such a manner as to maintain a steady moderate pressure on the part. 
The effect of this was not a continuous contraction of the whole part irritated, but a 
very rapid succession of jerking contractions, implicating its different fasciculi one 
after the other, by which a continuous approximation of the ends of all the fasciculi 
irritated was produced. Nowhere there were straight and zigzag fasciculi ; and it is 
plain that the straight were the shorter, or the contracted, the zigzag the longer, or 
relaxed. Indeed, if in any muscle in action, zigzags be observed which are not uni- 
versal, the fasciculi in which they occur must be in a relaxed state, compared to those 
having a rectilinear direction, and the phenomena of contraction cannot therefore 
be legitimately referred to them. If zigzags be requisite for contraction, there ought 
to be no straight fasciculi interspersed among them, but observation teaches us that 
there are. Besides, when the abdominal muscle of the Frog is laid on glass for obser- 
* In detached fasciculi, indeed, I have sometimes seen this (fig. 81.), but consider it the result of irregular 
contraction. 
t Hunter’s Works by Palmer, vol. iv. p. 261. 
