a d, c b, two ribs exhib. iting a part of the inter vening muscles, passing obliquely from bone to bone; by which direction of the muscles a mechan ical advantage is obtained as to the quickness of the motion, for the purpose of respiration or breathing.

Figure 16.

But there is a still more remarkable circumstance to be noticed in the structure before us, which shows the perfect foresight, and knowledge of mechanical laws exhibited in our frame. Do you not perceive that the sidelong action of these muscular strings a. b. must tend, while they pull the ribs together, to give a sidelong motion to the bones themselves, to cause the rib a. d, to move to the right and the rib c. b, to the left, and thus make them crowd against the places where their ends are inserted ?

A. It shews creative wisdom in our structure, that this difficulty seems evidently to have been contemplated. There are two sets of muscles employed lying one upon another, which not only increase the muscular power, but which, by sloping different ways, balance each other's sidelong tendency.

T. This single construction appears to me one of the most striking evidences of design in the animal frame. B. When the tendons, have occasion to make a sudden bend, as those do which come down and turn at the instep to raise the foot, what is to prevent them from rising up whenever they shorten and pull? One would suppose the sinews would spring off from the top of the foot, which would certainly be very awkward and unpleasant.

T. What if you should be told there are cross straps of ligament by which they are all confined down ; exactly as a mechanic would do in a similar case? The straps are just under the skin and are very slippery and smooth so as to bind the sinews in their places, but allow them a free motion. The tendons at the wrist are bound down in this manner by a band resembling a lady's bracelet, as exhibited in this figure.

Fig. 17.

a. the annular ligament of the wrist, under which pass the tendons of the muscles of the fin

gers.

B. What manifest design! One finds that to raise difficulties, is only preparing the way for some new demonstration of wisdom in this wonderful work of the Creator.

T. Can you mention any examples in the muscles, of that species of mechanical contrivance which is called the pulley?

A. Sometimes the situation of parts is such that a motion is wanted, where for some reason it is not so well to place a muscle, or bring it to act in the usual way. For example. A muscle is necessary to draw down the lower jaw, and this is done by a muscle inserted above the jaw. Nothing is more common in mechanics, than pulling one way to make the object move in the very opposite. But then the rope must pass through a ring or pulley. The sailor pulls down, and the cask comes He has a pulley above through which his rope is roven. The same contrivance is adopted in the present instance; the muscle called the digastric muscle, descends from the side of the head, and passes through a loop in the neck below the jaw, whence it ascends and is attached to the part to be drawn.

up.

B. I know not what contrivance could be more plain, nor how any one can look upon it, without being persuaded of a designing intelligence.

T. We have another example of the same kind in the trochlear muscle of the eye, from a latin work signifying a pulley.

ball

eye.

A. This muscle arises from the bottom of the orbit or socket, and then comes forward and passes through a loop on the inner edge of the socket, in advance of the level of the eye, whence it returns and is fastened to the of course, when the muscle contracts it rolls the It operates exactly in the same manner as a rope in a ship is carried over a block or round a stay, in order to make it pull in the direction which is wanted: or, as in raising one end of a stone pillar, the rope is passed forward of the object and then is reverted through a ring or pulley as at a, in the following figure, and attached to the weight to be drawn up.

T. There is quite as curious an example in the wing of the bird.

A. It is necessary the weight of the bird should hang below the wings, so as to balance the body in the air,

and prevent it from turning over;-for the weight of the body under the wings is the same as the ballast of a vessel under the sails. This requires that the muscles which constitute the principal part of the weight, should be disposed as much as possible upon the breast, and this principle we find to be observed. Every one who has seen a fowl upon the table, knows that upon the back, above the wing, there is only a mere skin. But the question arises, if the muscles, which are wanted to raise the wings, are situated beneath them, how are the wings to be elevated in the act of flying? As the muscle can only contract downwards, how is this to produce a rising motion? The contrivance which a mechanic would have employed is that which is actually adopted. The tendon of the muscle passes up from the breast, above the wings, and is there inflected through a ring or pulley, and fastened to the top of the wing bone, and is thus enabled to perform the service required. Fig. 21.

B.

How curious to notice the exact resemblance

in the manner in which the gaff of a vessel is drawn up on which the sail is spread, and that which is here employed in raising and expanding the wing!