"All my bones shall say, Lord, who is like unto thee, which deliverest the poor from him that is too strong for him, yea, the poor and the needy from him that spoileth him ?"-PSALM XXXV.

vessels do not sustain themselves upon the blood which they contain, but receive into their coats numerous capillary vessels by which they are nourished.

920. How much blood does the human body contain ? From twenty-five to thirty-five pounds. (See 623.)

921. How does the blood ascend in the veins, in opposition to gravitation?

In addition to the muscular coats of the veins, and the influence of muscular action upon them, there are in the veins numerous semi-circular valves, which are not found in the arteries. These valves extend from the sides of the veins in such a manner that they allow the free passage of the blood upwards, but a backward motion of the blood would expand the cup-like valves and stop the passage; so that the blood can only move in one direction, and that towards the heart.

922. How frequently does the total amount of blood circulate through the system?

The blood circulates once through the body in about two minutes. If, therefore, we estimate the amount of blood at twenty-four pounds, it follows that no less than twelve pounds of blood pass through the heart every minute; and it is estimated that if the blood moved with equal force in a straight line it would pass through one hundred and fifty feet in a minute.

CHAPTER XLV.

923. How many bones are there in the human body? There are two hundred and forty-six, and they are apportioned to the various parts of the body in the following numbers :

'Our bones are scattered at the grave's mouth, as when one cutteth and cleaveth wood upon the earth."-PSALM CXLI.

924. Of what substances are the bones composed?

One hundred parts of bone consist of

925. What are the uses of the bones?

They protect soft and delicate organs; they form a framework to which the organs are attached, and by which they are kept in their places; and they supply a mechanism, by which the motions of the body are produced, in combination with the muscles.

926. Why is the brain placed within the skull ?

Because that delicate and vital organ, being the centre and the root of the nervous system, requires a position of the greatest safety.

927. Why are the bones that constitute the vertebræ (back-bone) hollowed out, so as to form a continuous groove?

Because through that groove the spinal cord passes out from the brain. Being in the centre of that column of bones, the spinal cord receives from them a similar protection to that which the brain obtains from the skull.

928. Why is the head set upon the neck?

Because in that position it obtains the freest motion, can turn in any direction, and is placed relatively to the other parts of the body, in that situation where it acquires the greatest possible advantage.

929. Why are the eyes placed in the sockets of the skull? Because the bones of the skull afford protection to the delicate

H

"Thus saith the Lord God unto these bones, Behold I will cause breath to enter into you, and ye shall live:

and complicated. structure of the eyes, and supply points of attachment, and grooves, by. which the muscles are enabled to turn the eyes freely, and thereby extend the field of vision.

930. Why are the bones of the skull arched?

Because in that form they acquire greater strength, and hence the utmost degree of safety is combined with extreme lightness of material.

Fig. 54.-VIEW OF THE BONES OF THE THORAX, OR CHEST, SHOWING THE PROTECTION AFFORDED TO THE ORGANS OF CIRCULATION AND RESPIRA

TION.

A. The sternum, or breast-bone.

B B. The ribs, which rise a little from behind, and fall as they come forward, by which they acquire a greater flexibility.

CC. The cartilaginous points of the short ribs, by which their expansive and compressive powers are much increased.

DE. Part of the vertebral column, or back-bone.

931. Why are the bones of the skull divided by sutures (seams), with points which fit into each other like small teeth?

Because, by that arrangement, concussions of the skull, which might be fatal to the brain, are deadened, and injuries from accident greatly modified.

"And I will lay the sinews upon you, and will bring up flesh upon you, and cover you with skin, and put breath in you, and ye shall live; and ye shall know that I am the Lord."-EZEKIEL XXXVII.

932. Why are the heart, lungs, &c., placed within the chest? Because the functions of those organs require considerable space, while their importance in the system of life, renders it essential that they should be securely protected from the probabilities of accident.

933. Why are the heart and lungs enclosed for protection in a series of ribs, and not in a close case, like the brain?

Because, by the inflation and contraction of the lungs, their capacity is constantly changing. When man takes a moderate inspiration, he inhales about thirty cubic inches of air, and the lungs increase in size one-eighteenth of their whole capacity. Consequently, were they enclosed in a frame of fixed dimensions, it must needs be, to that extent at least, larger than is necessary, when the frame is made to dilate and contract with the capacity of the lungs

So perfect is the Almighty contrivance, that not only are the ribs made to protect the lungs, but, by their elasticity, and the contractions and dilations of the muscles which lie between them, they assist the lungs in their labours, and work with them in perfect harmony.

934. Why are the bones of the arms, legs, &c., made hollow?

Because lightness is thereby combined with strength. There is a provision by which, in the extremities of bones, where an enlarged surface is required, lightness is still combined with the necessary degree of strength.

The bones are made up of a cellular formation; and this generally occurs in parts which are much called into action, in the various movements of the body.

A. Lower part of the bone of the thigh.
B. Head of the bone of the leg.

C. The knee cap, showing its relation to the other bones, and the manner in which it is enclosed by the tendons seen at Fig. 58.

D. A pad of fat, lessening the friction of the bones, and modifying the shocks produced by jumping, &c.

"Again he said unto me, Prophesy upon these boues, and say unto them, O ye dry bones, hear the word of the Lord."-EZEKIEL XXXVII.

935. Why are the bones of the arms and legs formed in long shafts?

Because a considerable leverage is gained, by which the advantages of quickness of motion, and increase of mechanical power, are secured.

936. Why are the bones of the hands and feet numerous and small?

To

Because the motions of the hands and feet are very varied and complicated. There are no less than twenty-eight bones in one hand and wrist; and about as many in a foot and ankle. these are fastened a great number of ligaments and muscles, by which their varied compound movements are controlled. But for the complexity of the mechanism of our hands and feet, our motions would be extremely awkward, and many of the valuable mechanical inventions which now benefit mankind, could never have been introduced. The bones of the hands and feet are in number equal to one-half of the whole of the bones of the body.

CHAPTER XLVI.

937. What are ligaments?

Ligaments consist of bands and cords of a tough, fibrous, and ́smooth substance, by which the bones are bound together and held in their places, allowing them freedom to move, and supplying smooth surfaces over which they glide.

938. Why are the joints bound with ligaments?

Because the bones would otherwise be constantly liable to slip from their places.