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:--
Head 8 Ears 6 Face 14 Teeth 32 Back-bone and its base 26 Chest, &c. 26 Arms and Hands 64 Legs and Feet 62 Small moveable bones 8
[Verse: "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
Cartilage 32·17 parts Blood-vessels 1·13 " Carbonate of lime 11·30 " Phosphate of lime 51·04 " Fluate of lime 2·00 " Phosphate of Magnesia 1·16 " Soda, chloride of sodium 1·20 " ------ 100·00
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 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_.
[Verse: "Thus saith the Lord God unto these bones, Behold I will cause breath to enter into you, and ye shall live:"]
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_.
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.
C C. The _cartilaginous points_ of the short ribs, by which their expansive and compressive powers are much increased.
D E. 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_.
[Verse: "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.
[Verse: "Again he said unto me, Prophesy upon these bones, 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?_
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. To 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_.