The functions of bones in the human body differ in shape and size, covering equally diversified functions. On the basis of these characteristics it is divided into: long bones, when the length prevails on the other dimensions.flat or broad bones, when width or length prevail on the thickness; short bones, when the three dimensions are almost equal.
The bones are the hardest and most solid parts, and are designedas a frame-work or foundation for the attachment and support of the softer parts, to give form and symmetry to the body, and for the
purposes of motion and locomotion. When connected together in their natural order, they form what is called the skeleton.
The round bones are generally tubular, and the hollow is filled with a medullary substance called marrow, except at the ends or joints, where, instead of being hollow, the}- are usually enlarged,forming a kind of head, which consists of a sort of net-work structure, somewhat resembling honey-comb.
The flat bones, as those of the skull and the scapula or shoulder blades, consist of two thin tables, or
plates, united by the same kind of net-work structure.Like all other parts of the body (except the nails and hair), the
bones are supplied with blood-vessels, and nerves; and in their healthy state contain but little or no sensibility. But when m a state of inflammation they are extremely sensitive and painful.
The bones are covered with a very firm, thin and closely attached mem-
brane called the periosteum. Where this membrane covers the skull or cranium it is called pericranium.
The number of bones in the human body, including the teeth, is two hundred and forty, proper; though sometimes there are found in the thumbs and great toes what are called the sesamoid bones, increasing the number to two hundred and forty-eight.
The head (including the thirty-two teeth) contains sixty-three bones; the trunk fifty-three;
the upper extremities, or arms, sixty-four; and the lower extremities sixty.These bones are composed of both earthy and animal matter.
The earthy portion, which is mainly the carbonate and phosphate of lime,gives them their solidity and strength; while the animal portion,which is mostly gelatin, gives to them vitality, and prevents them
from being too brittle. If you will calcine a bone—in other words,burn it in a clear fire for ten or fifteen minutes, it will become white and brittle, the gelatin or animal portion having been destroyed,leaving the lime and chalk, or earthy portion.
Again, to show the animal without the earthy matter, place a small bone for a few days in dilute muriatic acid, say one part acid and five or six parts water,and the acid will have removed the earthy matter, by its affinity for the lime, leaving the bone unchanged in shape, yet so soft that it may be bent in any direction. In children, while the bones are soft,these two substances are nearly equal; but in adults there is a- much larger proportion of the earthy than of the animal matter in the bones. In the disease called rickets, or curvature of the spine, the earthy part of the bones has been more or less absorbed, leaving them soft and flexible.
How do you classify the Functions of bones in the human body?
The bones, like all other parts of the body, are formed from the blood, being at first only cartilage, and, while in this state, supplied only with the lymph or white portion of the blood. By and by they are
supplied with red blood, when the formation of true bone, or ossification commences, by the deposit of phosphate and carbonate of lime.
This process begins at certain points, called the points of ossifcation—generally in the center or middle of the bones, and gradually extends to the surface and ends. When ossification is complete there is still a gradual and constant change going on in the bones. They increase in size, the proportion of the animal matter decreasing and the earthy increasing, as the person advances in years, till in extreme old age the earthy substance so preponderates that the bones are extremely brittle and easily broken.
Such bones as form joints, as those of the arms and legs, have a reciprocal correspondence in their shapes at the points of union, the one usually being convex or round, and the other concave or socket-
shaped, so that they nicely fit together. They are also at these points spongy and porous, which renders them more elastic than if compact and hard, and are also covered with a cushion of cartilage, which acts like India-rubber springs, in preventing or diminishing severe jars and concussions.
There is around and about every joint what is called the synovial membrane, which secretes a fluid called synovia or
joint-water. This is for the purpose of oiling or lubricating the joints and surfaces of the bones and tendons, so that they may move smoothly upon each other, and avoid the friction consequent upon their action.