"That which is born of the flesh is flesh; and that which is born of the Spirit is spirit."-JOHN III.

939. What are tendons?

Tendons are long cords, of a substance similar in its nature to cartilage, by which the muscles are attached to the bones.

Fig. 56.-SHOWING A BALL AND SOCKET JOINT, AND THE MANNER IN WHICH LIGAMENTS ARE EMPLOYED TO HOLD BONES IN THEIR POSITIONS.

B. The socket, showing the ligament in the socket, which holds the head of the bone in its place, but allows it free motion.

C. Ligaments tied from bone to bone, giving firmness to the parts.

940. Why are tendons used to attach the muscles to the bones?

Because, by this arrangement, the large muscles by which the extremities are moved, may be placed at some distance from the bones upon which they act, and thus the extremities, instead of being large and clumsy, are small and neat.

941. How many muscles are there in the human body?

There are about four hundred and forty-six muscles that have been dissected and described, and the actions of which are perfectly understood. But there is probably a much larger number of muscles, and of compound actions of muscles, than the skill of man has been able to recognise.

"All flesh is not the same flesh; but there is one kind of flesh of men, another flesh of beasts, another of fishes, and another of birds."-CORINTHIANS XVI.

942. What is the constitution of a muscle?

Every muscle is made up of a number of parallel fleshy fibres, or threads, which are bound together by a smooth and soft tissue, forming a sheath or case to the muscle, and enabling it to glide freely over the surfaces upon which it moves.

A. Lower extremity of the muscle which draws the fore-arm towards the upper-arm, bends the elbow, raises the hand to the head, and is powerfully exerted in pulling, lifting, &c.

C. A muscle which gives off four long tendons, which pass under the ligaments of the wrist, one to each finger, and by which the fingers are bent upon the palm of the hand, as in grasping, &c.

F. Tendon of a muscle which draws the little finger and the thumb towards each other.

The ligaments may be seen enfoldthe finger-joints, and also crossing the wrist, underneath the tendons.

The muscles are compressed into tendinous cords at their ends, by which they are united to the bones.

They are arranged in pairs, having reciprocal actions-each muscle having a companion muscle by which the part which it moves is restored to its original position, when the influence of the first muscle is withdrawn, and the stimulus given to bring back the part.

943. Why can we raise our fingers?

Because muscles which lie on the fore-arm, and have their

"Thou hast clothed me with skin and flesh, and hast fenced me with bones and sinews."-JOB XI.

tendons fastened at the ends of the fingers, contract, and by becoming shorter, draw the fingers upward, and towards the

arm.

944. Why can we throw back the fingers after they have been raised?

Because the muscles at the back of the arm, whose tendons are attached to the back of the fingers, contract and restore them to their former position.

945. What degree of strength do the muscles possess?

The degree of strength of a muscle depends upon the healthy condition of the muscle, the amount of stimulus which it receives at the time of exertion, and the manner in which its powers are applied.

The great muscle of the calf of the leg has been found, when removed from a dead body, to be capable of sustaining a weight equal to seven times the weight of the entire body

But the contractile power of the living muscles is very great: the thigh bone has frequently been broken by muscular contractions in fits of epilepsy. And in cases where there has been a dislocation of the thigh, the head of the thigh-bone being thrown out of its socket, (Fig. 56) it has been found necessary to employ strong ropes, attached to a wheel turned by several hands, in order to overcome the contraction of the excited muscles, and to enable the operator to restore the bone to its place.

946. What is the stimulus which sets the muscles in action?

The muscles are excited to action by the nerves, which they receive from the spinal cord.

947. Why does it require the influence of the will to set the arms in motion?

Because the muscles which form their mechanism are voluntary muscles—that is, they are subject to the will of man, and influ

"And he took him by the right hand, and lifted him up; and immediately his feet and ancle bones received strength."-ACTS III.

enced by impulses directed to them through the nervous system by the mind, which is the governing power.

948. Why does the heart beat without any effort of the will?

Because the muscles of the heart are involutary muscles-that is, they are independent of the will, and receive a continuous nervous stimulus which is not under the controul of the mind.

A. A large ligament, which covers the knee pan, or moveable bone of the knee, by which the ends of the bones of the thigh and leg are kept from slipping over each other.

B. A muscle which passes underneath the cartilages of the ankle, and gives off four tendons, which are distributed to the toes, and by which they are extended in elongating the foot, walking, &c.

C. Part of the muscle which forms the fleshy bulb of the calf of the leg, and which terminates in the large tendon attached to the heel, called the tendon of Achilles.

D. One of the ligaments which bind the tendons and the bones of the ankle.

E. Arteries proceeding from the large vessel descending the leg, by which the toes are supplied.

949. Why are the muscles of the arms, &c., made subject to the controul of the will?

Because, as they supply the mechanism through which we adapt ourselves to our varying wants and circumstances, it was necessary that they should be placed under the controul of the mental power, and be moved only in accordance with man's necessities.

"If thou sayest, Behold, we knew it not; doth not he that pondereth the heart consider it? and he that keepeth thy soul, doth not he know it? and shall not he render to every man according to his works?"-PROVERBS XXIV.

950. Why are the motions of the heart, &c., made independent of the will?

Because, as the necessity for the heart's motion is fixed and unalterable, the constant motion of the heart could be best secured by giving it a fixed nervous influence, by which it might be unfailingly prompted to fulfil its functions.

If the movements of man's heart were subject to his will, he would be constantly required to regard the operations of that organ; and so large an amount of mental care and physical exertion would have to be employed in that direction, that man's sole work would be to keep himself alive. Hence we see the goodness of the Creator in giving life to man, and in keeping the vital impulses under his divine care.

CHAPTER XLVII.

951. What are nerves?

The nerves are branches of the brain and the spinal cord; they are distributed in great numbers to all the active and sensitive parts of the body.

952. What is the spinal cord?

The spinal cord is a long and large cord of nervous matter, which extends from the brain through a continuous tube formed by corresponding hollows in the bones of the back. It serves as a nervous trunk for the distribution of nerves, just as the aorta distributes branches of blood-vessels.

953. Why is the spinal cord placed in the grooves formed by the back-bone?

Being a very vital part of the system, and from the delicacy of its structure liable to injuries, it is set in the back-bone for protection; and so great is its security that it is only by force of an unusual kind that it can be injured.