Hygienic Physiology | Page 4

nostrils). | | |_Two Palate Bones. | | _ | | | Hammer. | | 3. EARS.................| Anvil. | | (6 bones.) |Stirrup. | | II. THE TRUNK (54 bones.) | _ | | Cervical Vertebr? (seven vertebr? of the | _ | neck). | | 1. SPINAL COLUMN........| Dorsal Vertebr? (twelve vertebr? of the | | | back). | | | Lumbar Vertebr? (five vertebr? of the | | |_ loins). | | _ | | | True Ribs. | | 2. RIBS.................|_False Ribs. | | | | 3. STERNUM (breastbone). | | | | 4. OS HYOIDES (bone at the root of tongue). | | _ | | | Two Innominata. | |_5. PELVIS...............| Sacrum. | |_Coccyx. | | III. THE LIMBS (124 bones.) | _ | | Clavicle._ | | Shoulder...|_Scapula. | | | | 1. UPPER LIMBS..........| | Humerus. | | (64 bones.) | Arm........|_Ulna and Radius. | | | _ | | | | _Eight Wrist or Carpal | | | | Bones._ | | |Hand.......| Five Metacarpal Bones._ | | |_Phalanges (14 bones). | | _ | | | Femur._ | | | Leg........| Patella. | | | |_Tibia and Fibula. | | 2. LOWER LIMBS..........| _ | | (60 bones.) | | Seven Tarsal Bones._ | | Foot.......| Five Metatarsal Bones._ | |Phalanges (14 bones).
_ | 1. Uses. _ | 2. Composition. | 1. FORM, STRUCTURE, | 3. Structure. | ETC., OF THE BONES | 4. Growth. | | 5. Repair. THE SKELETON | |_6. The Joints. | _ | 2. CLASSIFICATION OF | 1. The Head. |_ THE BONES. | 2. The Trunk. |_3. The Limbs. THE SKELETON.
I. FORM, STRUCTURE, ETC., OF THE BONES.
(See page 269.)
THE SKELETON, or framework of the "House we live in," is composed of about 200 bones. [Footnote: The precise number varies in different periods of life. Several which are separated in youth become united in old age. Thus five of the "false vertebr?" at the base of the spine early join in one great bone--the sacrum; while four tiny ones below it often run into a bony mass--the coccyx (Fig. 6); in the child, the sternum is composed of eight pieces, while in the adult it consists of only three. While, however, the number of the bones is uncertain, their relative length is so exact that the length of the entire skeleton, and thence the height of the man, can be obtained by measuring a single one of the principal bones. Fossil bones and those found at Pompeii have the same proportion as our own.]
USES AND FORMS OF THE BONES.--They have three principal uses: 1. To protect the delicate organs; [Footnote: An organ is a portion of the body designed for a particular use, called its function. Thus the heart circulates the blood; the liver produces the bile.] 2. To serve as levers on which the muscles may act to produce motion; and 3. To preserve the shape of the body.
Bones differ in form according to the uses they subserve. For convenience in walking, some are long; for strength and compactness, some are short and thick; for covering a cavity, some are flat; and for special purposes, some are irregular. The general form is such as to combine strength and lightness. For example, all the long bones of the limbs are round and hollow, thus giving with the same weight a greater strength, [Footnote: Cut a sheet of foolscap in two pieces. Roll one half into a compact cylinder, and fold the other into a close, flat strip; support the ends of each and hang weights in the middle until they bend. The superior strength of the roll will astonish one unfamiliar with this mechanical principle. In a rod, the particles break in succession, first those on the outside, and later those in the center. In a tube, the particles are all arranged where they resist the first strain. Iron pillars are therefore cast hollow. Stalks of grass and grain are so light as to bend before a breath of wind, yet are stiff enough to sustain their load of seed. Bone has been found by experiment to possess twice the resisting property of solid oak.] and also a larger surface for the attachment of the muscles.
The Composition of the Bones at maturity is about one part animal to two parts mineral matter. The proportion varies with the age. In youth it is nearly half and half, while in old age the mineral is greatly in excess. By soaking a bone in weak muriatic acid, and thus dissolving the mineral matter, its shape will not change, but its stiffness will disappear, leaving a tough, gristly substance [Footnote: Mix a wineglass of muriatic acid with a pint of water, and place in it a sheep's rib. In a