32 
FIRST CLASS OF THE VERTEBRATED ANIMALS. 
a/!tion experiences any mechanical disadvantage, it arises from the mode of insertion, 
and not from the composition of the muscle. This is not the case with the two other 
kinds of simple muscles, the radiated and penniform. 
The radiated muscles are those which have their fibres disposed like radii of a 
circle, and which proceed from a base more or less extended, while they incline to- 
wards each other, and are inserted in a s'.nall tendon. 
The penniform muscles have their fibres disposed in two rows, unitin'^ in a middle 
lino, and forming angles more or less acute, so that they resemble in some degree the 
arrangement of the feathers in a quill. The tendon forms the continuation of this 
middle line. 
It may be easily perceived that, in the two last-mentioned kinds of muscles, the 
total or resulting force is less than the sum of the component forces ; and that, if wo 
take successively the Icngtlis of every two fibres, which unite in producing one angle, 
as the measures of their individual forces, the diagonal of the ultimate parallclograra 
which may be formed thereon will represent the entire resultant, m quantity and 
direction, belonging to the fibres of the whole muscle. 
When several muscles unite in one common tendon, tho result is called a com-^ 
pound muscle. Those muscles may be similar in their nature, but sometimes they 
are formed of very different kiurls, such as the radiated and the ventriforra uniting to 
form one compound muscle. Wo may, then, estimate the particular action of each 
according to the preceding observations, and the total action can then bo estimated 
according to tlie degree of their inclination. Other muscles, again, are styled comp/i- 
cated: these may have only one belly with divided tendons; or they may have several 
fieshy parts, wherein the tendons are interlaced in several ways. 
The absolute force of the muscles is determined from these several dispositions; but 
it is their insertion which determines their real effect. Tiie muscular insertions may 
be referred to eight distinct classes: — 1st, the fleshy envelope; 2d, the sphincter or 
ring; 3d, the curtain; 4th, the rotatory; 5th, the rope; 6th, the lover of the first 
kind; 7th, the lever of the second; and 8th, of the third kind. The first four have 
a striking similarity, in their being all formed of a girdle, or portion of a girdle, which 
contracts upon the sun‘ounding parts. 
1 . The diaphragm and abdominal muscles arc instances of the fleshy envelope. 
Being destined to compress thesoft parts contained in a certain cavity, they envelope that 
cavity in every direction, in the form of membranes or bands. When all the fibres act 
siinuitanoously, it is for excretory purposes ; but they usually act alternately, a:id then 
the effect is to enlarge one cavity and to diminish the other. Thus, at each iuspii'a- 
tioii the abdomen becomes wider and shorter, while the contrary happens on each 
expiration. The heart, arlcries, and intestines, have muscles of this'kiud; and the 
muscles moving the tongue in Man and Beasts must also be referred to this class. 
2. The sphincter muscles are calculated to widen or contract some soft aperture. 
Some of them surround the orifico like rings, and others are inserted in a manner, 
more or less directly, upon the •edges of the opening. If the muscle bo uniformly dis- 
tributed around the orifice, it always preserves its figure, and is dilated or contracted 
always in the rame manner. But when these muscles have different directions, and 
make different angles with the edges they have to move, the form of the aperture is 
v(n*y variable, as wc may see in the lips of iM.m. No animal possesses so great a mobi- 
lity of this pai't, and none can therefore possess so expressive a physiognomy. 
3. The curtain muscle is scon ii» the eyelids of lilan and other IMammalio. When 
these muscles arc placed in the body of the membrane, which is destined to cover some 
other parts, their structure is such as we have just described; but when they are 
situate externally, they have the form of very complicated pullics, as will be explained 
when we come to treat of the Eye in Birds. 
4. The rotatory motion of the muscles may bo seen in the means by which the globu- 
lar mass of the eye is rolled and supported on every side. 
5. The rope muscle has already boon alluded to, in speaking of the larynx, and 
may be rogardi>d as the most advantageous form in which a muscle can be applied. 
6. 7, 8. ^^’hen a bone intended to be moved is articulated at any particular point, it 
cannot be elevated or depressed iii a direct line, but must be* considored as a lever 
having its fulcrum in the articulation. Thu bone forms .a lover of the first kind when 
tlio articulation is between the two extremities, and the muscles arc placed at one of 
them, as wc may observe in the muscles attached to the olecranon and heel-bone. 
But the most usual case is when the articulation is at one of the extremities of the 
bone; and then the most favorable position for the muscle is when it rises from 
another bone parallel to that which it has to move, or which forms with it only a very 
small angle. ThU is rhe case with the muscles between the ribs {iittcrcosiale^)^ and 
several others. Yet these muscles possess a degree of obliquity which considerably 
diminishes their power. The muscles closing the mouth of Man may also be com- 
pared to those just mentioned with respect to their small obliiiuiLy; but they are in- 
serted much nearer to the point of support than tlie former, a circumstance which 
also considerably dirainiahes their force. 
The most usual kind of insertion is where a miijcle attached to one bono is inserted 
into another, which last is articulated either mediately or immediately with the first, 
and may be extendofl until they both form a Unu, or inflected so as frequently to make 
a very small angle. This mode of inseiitioii appoiu's to be the roost disadvantageous 
of all in respect to mere force, on account of the obliquity of the insertion when the 
moving bone ia extended, and also on account of its proximity to the fulcrum. The 
first inconvenience is partly corrected by tho heads of the bones. Their articular 
extremities aro usually enhtrged, so that the tendons of tlio muscle, by turning round 
a convexity, in order to be inserted below it, form more obtuse angles with the lever, 
or body of the bone, than would be practicable if the head did not e.xifit. Uy this 
means tho obliquity of their insertion is diminished, and rendered less variable. 
The proximity of the fulcrum was necu-ssary to prevent the members from being 
moustrottdy large in the state of flexion, but particularly for producing a prompt and 
complete flexion. As the muscular fibre loses only a determinate fraction of its length 
by contraction, if the muscle were inserted at a greater distance from tho joiiii;, the 
moveable bone would only be approximated to the other by a small angular quantity. 
On the contrary, by inserting it near the apex of the angle, a very small contraction 
occasions a considerable approximation. Velocity is gained in proportion as the space 
through whidi the muscle acts is diminished. In this manner, muscles of this kind 
exorcise a power which surpasses all imagination. 
There are many instances of muscles inserted at a considerable distance from the 
fulcrum, especially in tho short bones, which must be completely inflected. The ver- 
tebr® and phaLiuges of the fingers arc in this situation. Muscles extended from the 
one to the other of those bones would not have produced a sufficient degree of flexion. 
In the phalanges, the fingers would have been two thick. It was also necessary that 
the tendons of these muscles should be attached to the bones over which they pass. 
If this were otherwise, it would happen that, whenever the phalanges were bent so as 
to form an arc, the muscles with their tendons would remain in a straight line, and 
form its cord. We may hence perceive the necessity of the annular ligaments, the 
sheaths and perforations. The last-mentioned arrangement occurs solely in tho fluxions 
of the fingers and toes of iilan, Quadrupeds, and some other animals, and consists in 
the muscles which have to extend farthest being placed near to the bones, while thoir 
tendons, perforating those of the muscles, are inserted at a shorter distance, and lio 
over the .first. When there are only three phalanges, there is but one perforation. 
The muscles moving the tail in the Quadrupeds arc placed at a great distance from it; 
but their long and slendjr tendons are inclosed in sheaths, which they do not leave 
excepting immediately opposite the points into which they are to be inserted. 
The whole of the Mamtnalia have flie upper jaw fixed to the skull ; and 
the lower one is composed of only two pieces, articulated to the tempo- 
ral bone, by a projecting part [called the condyloid process.] 
By the elongation of tho condyles, which fit into the z)'gomatic process of the tem- 
poral bone, this joint is nearly restricted to tho motions of a hinge, alternately raising 
and depressing, while the lateral motion is only just sufficient for the grinding of the 
food. 
There is a single or double bone, found in most Mammalia, called the intor-maxil- 
lary bone, but of which Man is entirely destitute. In these animals tho upper jaw- 
bones do not touch each other under tho nose, nor do they contain all tho teeth, hut 
the intur-raaxillary bone is wedged in between the former, and contains the incisive 
teeth of those animaU possessing them. The size of this bone varies surprisingly in 
the several orders and genera of Mammalia, being small in the Walrus and many Car- 
nossiers, but large in tho Beaver, Jlarmot, Hippopotamus, and Cachalot, but especially 
in the Wombat. In tho Ornithorynchus it is constructed of two pieces in the form of 
hooks. This bone is seen to exist in animals altogether destitute of tooth, and is 
also found in such Ruminantia as have no incisive teeth in the upper jaw. Some ana- 
tomists have doubted whether the upper jaw-bones and inter-maxillary bones are not 
the same, and that the latter is merely the anterior or incisive portion of the former. 
Thu latter opinion appears to bo the more probable, as the division is found in tho 
human fmtus, while, in some quadrupeds, the two bones are frequently seen to coa- 
lesce. Tiio lower jaw surpasses all other bones in the variety of its forms among the 
diflurent ^lammalia. It possesses very strong projections on the under side in the 
Wombat; .and we may remark in tho Cercopilhecus Beelzebub, and other Brazilian 
IVIonkeys, a remarlcablc lateral development of the bono, which assists tho larynx in 
the emission of that extraordinary deafening sound peculiar to these animals. In the 
Ornithorynchus, the anterior part of the lower jaw is shaped like a shovel. 
An intimate relation may be observed between tho kind of food with which an ani- 
mal is nourished, and tho motions performed by its lower jaw; and these again are 
greatly influenced by the form of its condyles. Thus, Mammalia living on vegetables 
possess a power of moving their lower jaws from side to side, so as to produce that 
grinding effect necessary for pulverizing and dividing grain, and for bruising grass. 
These animals are in this way able to move their lower jaw in almost every direction, 
by the form of the condyle, and of the cavity to which it is articulated. On the con- 
trary, with the Carnassiors, wo find that the lower jaw is altogether incapable of any 
other motion than simply downwards and upwanls, being destitute of that lateral 
grinding motion attendant on mastication in its most perfect form. Thus, while the 
teeth of the Herbivorous quadrupeds may be compared to the stones of a mill, the move- 
ments of the teeth, or rather tusks, in the Carnivorous quadrupeds greatly resemble 
the dividing motion of scissors. 
The neck consists of seven vertebrte, one species excepted [the tbree- 
toed sloth] which bus nine. 
A great variety is found in tho number of their vertebr®, excepting those of the 
neck. In the Cetacea, where the nock is very short, the bodies of the Cervical Ver- 
tebr® are extremely thin, and form by anchylosis one hone ; so that the original number 
of vertebrar, with their processes, can scarcely be perceived. In Quadrupeds having 
long and flexible necks, such as the Camel, and Camelopard, the spinous processes of 
tho vertebrre of the neck are small, or they are nearly obliterated. A peculiar sub- 
stance of great strength, called the Ugamcnlnmnncha:, is attached to the necks of the 
larger quadrupeds. By mcAna of this elastic body, the great weight of the head is sup- 
porteiL In the Elephant, it is of a very great size. The short-neckcd Cattle have 
double tr.ansveraa processes, and in the bodies of tho Cervical Vertebra*, both of Rumi- 
nating animals and Horses, there is a longitudinal rtdgo running along tho front. With 
Carnivorous animals, the ligamcnittm nuchts is small ; and as the pendent position of 
their heads require strong muscles for their support, the Cervical Vortebrjc have thoir 
transverse processes very large and flat, both in tho front and back, and thus afibrfl 
places of attachment for tho muscles of the neck, as well os for those which contribute 
to open their mouths. 
The length of the neck docs not depend upon the number of the cervical verte- 
brae; for, as wc have alrcaily observed, this is nearly always the same in most 
fupeds. In general, we find the length of the neck to be such, that, when it ^ 
added to the head, their united lengths am exactly equal to the height of the anim^i 
from the ground. Were this otherwise arranged, quadrupeds could not easily have 
reached cither the herbs on which they feed, or the water they must drink. 1 
hulk of the head, in all those animals where this rule is observed, is very nearly 
an inverse proportion to the length of tho neck, else the muscles would bo unable t® 
elevate the bead. This rule, however, is not adhered to in such animals us lift ikorf 
