MUSCLE. 
the transverse lines being often irregular, 
broken, or faintly marked. And we may also 
discern a clue to the meaning of the structural 
condition which is found in the complicated 
muscles of the higher animals. The essential 
contractile material is the fibre, and its mass 
is accurately proportioned to the power de- 
manded. If this is below that of a single 
elementary fibre, the fibre is reduced in pro- 
portion ; if more is required than one fibre can 
Supply, the size of this is not increased but its 
number multiplied. The point at which an 
increase in number supersedes one in size, is 
that which has been already stated to be the 
average bulk of the fibre. This differs in the 
different classes of animals, and corresponds 
with the demand there may be in each class 
for vascular and nervous supply. For by the 
very constitution of the contractile materal, it 
can receive neither vessels nor nerves into its 
interior substance, and therefore it must be 
itself subdivided further and further in pro- 
portion to the amount of these which are to be 
im contact with its surface. 
In the compound organs termed muscles, 
the fibres are usually disposed in parallel sets 
of 10, 20, 30, or more, surrounded and held 
together by a delicate areolar tissue, which 
penetrates more or less among the individual 
fibres, but does not necessarily invest each one 
of them from end to end, as it is frequently 
described to do. Where the fibres are not very 
large, it is often difficult to discern any areolar 
tissue at all in connexion with them. ‘These 
first sets admit of considerable motion on 
one another, in consequence of the looseness 
of their areolar sheath. Like the elementary 
fibres themselves their figure is polygonal, for 
= in their turn are arranged (if the muscle 
be large enough) into secondary sets, and are 
flattened by being pressed together. These 
= are aggregated into tertiary sets, and 
se into still larger ones, according to the 
size of the particular organ. All these sets 
partake of the polygonal figure of the elemen- 
tary fibres; except the portion that forms a part 
of the general exterior of the muscle, which is 
usually more or less rounded. As the packets 
of fibres are larger, so their angles are more 
rounded, and their surface covered with a more 
abundant areolar sheath, and they approach, 
in fact, to the condition of a perfect muscle, 
which is itself included in an envelope of 
areolar tissue. Their angles are thus rounded 
in consequence of the greater quantity of areo- 
lar tissue, and of the larger size of the vessels 
and nerves that occupy their intervals. For the 
same reason the elementary fibres themselves 
* are less sharply angular, when very small, as in 
Birds, because the vessels accompanying them 
are proportionally more abundant, and occupy 
more space in their intervals. 
‘ arrangement of the elementary fibres 
into these packets has received more attention 
than its importance deserves, and anatomists 
have endeavoured to afhx definite names (fasci- 
culi, lacerti, &e.) to certain sizes of them. 
But no division of this kind is to be found in 
nature. It may be safely said that packets of 
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315 
every possible bulk exist from the simple set of 
two or three fibres, to those of many thou- 
sands, these last being subdivided with the 
greatest irregularity. And it is only in muscles 
possessed of some thickness that any such 
package in sets is to be met with. The ab- 
dominal plane muscles, which contain such an 
arrangement in the larger animals, are, in the 
smallest, composed of a single unbroken layer 
of elementary fibres. A similar diversity exists 
between rnuscles of different size and shape in 
the same animal. In the gluteus maximus, 
which is liable to pressure and change of 
position from its peculiar situation, the fibres 
are made up into lacerti, about one-quarter of 
an inch thick, surrounded with a dense areolar 
sheath, and attached loosely to one another ; 
while the glutei situated underneath are, like 
the psoas, unprovided with such dense septa 
of areolar tissue, and seem more uniform 
throughout. 
From these and many other considerations 
which might be adduced, it may be clearly 
seen that the mere aggregation of the elemen- 
tary fibres in a muscle into larger or smaller sets, 
is determined solely by its own peculiar cir- 
cumstances and exigencies, and is not of a 
nature to demand particular description in so 
general an account as the present. 
The direction of the elementary fibres of vo- 
luntary muscles is usually straight, between 
their points of attachment, which are always 
some form of the fibrous tissue. This tissue 
may be so arranged as that the sets of mus- 
cular fibres passing from it, may be either 
ers or oblique to one another, but the fibres 
orming any one set are generally placed in a 
arallel series. If the fibrous tissue form a 
aminar expansion on the surface of a muscle, 
the muscular fibres pass off from it obliquely, 
either to a similar expansion on the opposite 
surface or to atendon. If they arise from an 
extensive surface of bone (i. e. of periosteum) 
they conduct themselves in a similar fashion, 
and also if they pass from a line of tendon or 
of bone. In all these cases the muscle may 
be styled penniform. If a thread or sheet of 
fibrous tissue dip into the interior of a muscle, it 
gives origin to the muscular fibres on both 
sides, and they diverge from it obliquely: 
such a muscle is styled doubly penmiform. 
When several such sheets enter the muscle at 
both extremities, and give attachment to the 
fibres obliquely placed in the intervals, the 
muscle is styled compound penniform, as the 
deltoid. 
One result of the varied arrangement of the 
tendinous fibres with regard to the muscular, 
is the production of symmetry and beauty of 
form ; a second is convenient package; a third 
is the adaptation of the particular muscle to the 
kind and amount of exercise which is required 
of it. Where a great mass of fibrous tissue runs 
into a muscle, the number of fibres and their ob- 
liquity is very much increased, while the length 
of each is diminished ; and, as a general result, 
the power of such a muscle is augmented 
while the extent of its contractions is limited. 
The same mass of contractile material may be 
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