In the Human Frame Strength sacrificed to Velocity. 357.

On many occasions velocity again is obtained by the numerous joints, which move in concert to one object. Thus when a straight blow is struck, the hand moves forward with greater velocity than is communicable by a single set of muscles; at one and the same instant the humerus is raised, and the fore-arm depressed; and the fist, projected by two forces, moves in the diagonal between both impulses.

The only instance, in which the third kind of lever is employed in the human frame, and velocity sacrificed to power, is to be found in the foot:-the tendo Achillis is attached to the long arm of that lever, which raises the weight of the body upon the ball of the great toe.

The strength of muscular fibre is unknown: but it is supposed that a muscle, the section of which would present a surface an inch square, might exert a force equal to five hundred pounds. It seems likely that there may be an original difference in the quality of muscles;' and that some of greater volume are essentially weaker than others less in bulk but of more rigid fibre. Much, however, depends upon the energy, with which the will operates. During phrenzy, a slight and feeble frame is often found capable of going far beyond the most powerful efforts of the strongest man, when acting under less excitement.

The continued action of a voluntary muscle must metaphysically depend upon successive impulses of the will, repeated at infinitely short intervals; and a curious observation of Dr. Wollaston's makes it appear, that in a continued muscular effort, the renewal of the muscular contractions may be even appreciable by the senses.

7

* Phil. Trans. vol. c. p. 5.

358 Of the erect Posture, and of Locomotion.

The body stands, when erect, on the same principle as a modelled image of similar weight: its position is secure, as long as a perpendicular drawn from its centre of gravity would fall within its base. The muscles support the frame erect, by keeping the joints rigid in any attitude, which may be assumed involving the preceding condition. The securest posture, that could be given to a model, would be the securest for the human body. What renders the attitude of standing practically so firm in a living person is the power we have of anticipating the side, on which it will be necessary to make resistance, and of increasing the length of the base, on which we rest, in the direction, in which violence is threatened.

If a person standing erect be killed instantaneously, he drops prone on the ground: the body falls forwards, because the greater part of its weight is naturally placed before that column, which, in the case supposed, suddenly gives way, at every point where there is a joint. The tendency of the body to fall forward seems provided against accidents of a less grave character, to which we are occasionally liable: we thus fall, when we lose our balance, against objects, which we see, and towards which our hands and arms are readily advanced to break our fall.

In the more violent kinds of locomotion, in vaulting, and running, the body is thrown forward by the re-action of the soil, that follows the sudden pressure made upon it by a simultaneous contraction of the extensor muscles of the ankle, knee, and hip.

The insecurity attending the preceding methods of progression is avoided in walking, in which the support of the body is alternately transferred from one leg to the other, and one foot is always planted on the ground.

When we purpose to step forward in walking, we

Character denoted by muscular Action.

359

begin by inclining the body to one side, so that it rests upon one leg. The opposite limb is then advanced, the knee being at first slightly bent in order to detach the foot from the ground. The hip-joint of the first limb is finally extended, by which means the trunk is propelled forward, so as to be received the next instant upon the limb which was advanced. Each step may thus be resolved into three elementary movements.

The different gestures of the body, like the tones of the voice, betray the presence of strong emotion. In anger the step is hurried, as the accents are; the hand is unsteady, when the mind is agitated, is spread abroad in wonder, is clenched in agony.

Voluntary muscles are observed to take a bias towards those actions, which they have several times repeated. The hard-working mechanic, when he divests himself of the dress and implements of his trade, betrays by the carriage of his limbs the occupation, to which his working day labours are devoted.

Individual character is formed by the adoption of peculiar habits of thought and feeling: now each mood of thought and feeling has its corresponding sign in some change of feature: but changes of feature or changes in the expression of the countenance are produced by muscular action; and the muscles of the face like those of the trunk and limbs unconsciously take a tone from the actions, in which they are frequently employed :-thus the prevailing character of the mind becomes faithfully pourtrayed in the lineaments, which the countenance wears, even when the mind and the features are in perfect re

pose.

GENERATION consists in the growth of a seed, or germ,, or embryo upon a living surface, from which it separates, when it has become capable of independent existence. In following the ascending 'scale of organization either in plants or animals, the genital system is found to resolve itself into two parts, in one of which the germ grows, while in the other a substance is secreted, the contact of which appears to fecundate the germ. When these organs are met with in the same individual, the plant: or animal is termed an hermaphrodite; when in different individuals, the distinction of sexes into male and female arises.

In human beings, the female organs consist of the ova ries, the uterus, the vagina: the male organs consist of the testes, the prostate gland, the glands of Cowper, the penis.

The ovaries, which form the essential part of the fe male organs, are two flattened oval capsules, that are lodged in the fold of peritoneum, which forms the broad ligaments of the uterus. When cut into, they are found to consist of a loose succulent texture, in which there are several small cysts, termed corpora Graaffiana, containing a serous liquid; their number is from fifteen to twenty; they vary in size, the largest being about four lines in diameter. At an early age the surface of the ovaries is smooth; as life;

advances, it becomes marked with numerous scars or cicatrices. At the same time one or more of the cysts are commonly found filled with a yellowish material of the consistence of curd; this appearance constitutes a corpus luteum. The ovaries are supplied with blood by the spermatic arteries, with nerves from the spermatic plexuses: on their removal the sexual passion is entirely destroyed.

The uterus is a hollow fleshy organ placed between the bladder and rectum. Its texture is fibrous, but much firmer than muscular substance. The broader portion or body of the uterus contains a triangular cavity, from two corners of which a tube termed the Fallopian tube leads towards the ovaries. The Fallopian tubes are about five inches in length; they become tortuous and enlarged towards their ovarian extremity, which is open, and fringed with irregular filaments or fimbriæ, that are capable of attaching themselves to the ovaries.

The third corner of the cavity of the uterus leads by a long channel called the cervix uteri into the cavity of the vagina. The aperture of the uterus is called the os tincæ.

The vagina is a mucous canal surrounded by a thick vascular membrane. At the orifice are the labia and clitoris; and in virgins a crescentic fold of membrane, termed the hymen, is found, leaving a narrow aper

ture.

The testes, which form the organs essential to the genital system in the male sex, are glandular bodies. Either testis is suspended in the scrotum by a part called the spermatic chord, which consists of the spermatic artery and veins, of the spermatic plexuses of nerves and absorbents,