the centre, which is called the belly of the 
muscle. The second kind of simple muscle 
is ilat, and has parallel fibres. These form 
a sort of fleshy membrane, which, instead of 
terminating in small tendons, ends by apo- 
neurosis, or a kin 1 of tendinous membrane. 
In the action of muscles it appears that the 
elementary fibres, all individually, exercise 
the same power at the moment of contrac- 
tion; but Lae sum total of force is directed 
4 >y the manner in which these fibres are dis- 
posed* or the .ituation of the whole muscle. 
It is obvious then, that in either kind of these 
simple muscles above described, the total 
action is equal to the sum of all the parti- 
cular actions, which however is nut the case 
with the two other kinds of simple muscles,, 
the radiated and penmform. Muscles are 
said to be radiated, when the fibre: of which 
they are composed are disposed like the 
radii of a. circle, which, proceeding from 
a base of a greater or less magnitude, in- 
cline towards each other, and are inserted in 
a small tendon. 
Penniform muscles have their fibres ar- 
ranged in two rows, which unite in a middle 
line, and form with each other angles more 
or less obtuse, assuming the appearance of 
the feathers of a quill. Their tendon is a 
prolongation of this central line. 
in these two last kinds of muscles the re- 
sulting force must necessarily be less than the 
collective sum of the component forces: it is 
only equal to the sum of the diagonals of the 
parallelograms, which are formed from every 
two fibres that unite in the production of 
one angle. 
Compound muscles are produced by the 
union of several in one common tendon. 
Sometimes these uniting muscles are of a 
similar nature: at others the compound muscle 
is formed by an assemblage of various kinds, 
as the radiated, the ventritbrm, and others. 
There are some muscles with only one 
belly with divided tendons ; others have se- 
veral fleshy parts and tendons interlaced in 
various ways. These last may be denomi- 
nated complicated muscles. 
Muscular origin and insertion may be con- 
sidered as of eight distinct kinds. A muscle, 
or muscles, may be destined to compress the 
soft parts contained in a cavity, which is 
then enveloped by the muscular fibres in 
different directions, in the form of mem- 
branes or bands. Such is the arrangement 
in the abdominal muscles and diaphragm of 
the human species; such is the disposition of 
the muscles of slugs, other moliusca, and 
naked worms, which can contract themselves 
in every direction. When a number of such 
muscles act in conjunction, it is for the pur- 
pose of expelling some matter from the 
body, as excrement, or ova; their more usual 
action however is alternate, and then their 
effect is to increase one of the diameters of 
the cavity they surround, and diminish the 
other. Thus, for example, during every in- 
spiration the abdomen becomes wider and 
shorter, while exactly the contrary takes 
place on each expiration. In like manner 
slugs and leeches lengthen and shorten them- 
selves, by first moving their annular, and 
then their longitudinal muscles. 
Upon this principle likewise, those muscles 
act which are destined to lengthen or shorten, 
and to relax or compress, any soft part ; such 
as the tongue of man, or the horns of snails. 
O 
COMPARATIVE ANATOMY. 
The heart, the arteries, the intestines, and 
other organs, are furnished with muscles of 
this kind. 
Some muscles are calculated to enlarge or 
diminish a soft aperture ; of these some sur- 
round the orifice as the sphincters; others 
are inserted more or less directly in the mar- 
gins of the apertures. When they are uni- 
formly extended round the orifice, such ori- 
fice preserves its figure, and is always dilat- 
ed or contracted in the same manner. The 
eyelid of the moon-fish, and the anus of the 
snail, present examples of this species of 
muscular motion. When these muscles are 
inserted in different directions, the form of 
the aperture is very variable ; as for instance, 
in the lips of man. The expressive variety 
of the human physiognomy arises in a great 
measure from the great mobility of this part. 
Another employment of the muscles is to 
extend and fold back in the manner of cur- 
tains, membranes that furnish coverings to 
certain parts; such as the eyelids of man, 
quadrupeds, and birds. When such muscles 
are in the bodies of these membranes, their 
descriptions are the same as above described; 
but when their situation is external, they 
form complicated pulleys. 
Again, muscles are employed in the act of 
turning or rolling a globular mass, which, 
although free, is supported on every side, as 
the human eye in the orbit, or the mouth of 
a snail in its' head. The muscles surround 
such parts in the form of a hoop, and the 
body which they move is turned to that 
part in which the muscle contracts with most 
vigour. 
These four modes of action may all be re- 
ferred to that of the sphincters or circular 
muscles. 
The following mode in which the muscles 
perform their action may be compared to 
the action of ropes, drawing a resisting ob- 
ject ; the muscular fibres pulling in the di- 
rection in which the motion of the part ope- 
rated upon is to be performed ; or if the 
muscles diverge, an equal quantity of action 
is produced on either side, and the resulting 
force is employed to still more advantage. 
Of the first kind of action, the sterno-hy- 
oideus and genio-hyo'.deus form examples, 
and the motions ot the mylo-hyoideus and 
scapulo-hyoideus are instances of the se- 
cond. 
When the bone on which the muscular 
agency is displayed, cannot be elevated or 
depressed all at once, it must then be re- 
garded as a lever, the articulation affording 
the fulcrum. 
When the articulation is between the two 
extremities, and the muscles are situated at 
one of them, the bone forms a lever of the 
first rank ; such is the ease in the mandil le 
of the cray-fish ; an example of a similar 
kind is like wise furnished by the olecranon 
and os calcis, with their respective muscles ; 
but the most remarkable is, the tibia of those 
birds called grebes and divers ; the long apo- 
physis of which, raised above the knee, 
serves as a substitute for the patella. 
But the most common case of muscular at- 
tachment is, that in which the ai ficuiation is 
at one extremity of the bone ; then the most 
favourable position of the muscle is, when 
it originates from another bone parallel to 
that which it has to move, or when it forms 
with the latter only a very small angle ; such 
415 
is the case with the intercostales, interspi- 
nales, and intertransversi ; and the muscles 
which draw together bones of a fan-like 
shape, as the wings of the flying dragon. 
The muscles which close the mouth of man 
and the bill of birds may be also compared 
to the preceding ; these however are in- 
serted nearer to the point of support, and 
by consequence their force is diminished. 
The last and most usual mode of insertion 
is, when a muscle united with one bone is in- 
serted into another, which last is articulated 
with the first, and may be extended so as 
to form together a right line, or bent into a 
very small angle ; this mode is the most 
disadvantageous, on account ot the extreme 
obliquity of the insertion when the moveable 
bone is extended, and because of its proxi- 
mity to the fulcrum ; this inconvenience, 
however, is in some measure obviated by 
the heads of bones, or enlargements of their 
articular extremities ; so that the tendons, 
turning round a convexity in order to be in- 
serted below it, form more obtuse angles. 
It was necessary that the fulcrum of mo- 
tion should be near, to prevent the members 
from being inordinately large, and likewise 
for the production of a ready and com- 
plete flexion, as the muscular fibre loses 
only a determinate fraction of its length 
in contraction. Examples are afforded of 
muscles inserted at a great distance from, 
the fulcrum : birds have one which extends 
from the top of the shoulder near to the 
carpus ; this however happens because all 
the angle formed by the radius and ulna is, 
in these animals, occupied by a membrane in- 
tended to augment the surface of the wing. 
It is in consequence of the small contrac- 
tion of the muscular fibre, that the short 
bones in which complete inflexion is re- 
quired, are moved by muscles attached to 
bones at a distance: the vertebra and pha- 
langes of the fingers are in this situation. 
Muscles extended from one to the other of 
these small bones could not have produced 
a sufficient flection : besides, in the phalanges 
they would have made the fingers dispro- 
portionately thick : it is also necessary that 
the tendons of these muscles be fixed down 
to the bones over which they pass ; otherwise 
whenever the phalanges were bent, the 
muscles and tendons would remain in a 
straight line like the string of a bow ; hence 
the utility of the carpal ligaments, the 
sheaths, and perforations. In animals that 
have but three phalanges, as in man, there is 
but one perforation ; but birds, which have 
one toe with four and another w'ith live pha- 
langes, have two perforations and conse- 
quently three muscles, — one perforated, one 
perforating and perforated, and one per- 
forating. 
Those vertebra which have much motion, 
for example, those of the neck in birds, and 
of the tail in quadrupeds, .have likewise very 
distant muscles ; bu. their long tendons are 
enclosed in sheaths, which continue to bind 
them, until they arrive opposite the place of 
termination. 
External form as an indication of 
THE NATURE OF IKE SENTIENT 
ORGANIZATION. 
In the general description which w'e have 
already given of the skeleton, the head of 
vertebral animals was said to be capable of 
