Physiology is the science which treats of the uses of the various parts of the body.

Anatomy is the science which treats of the structure of the various parts of the body.

The organs and other parts of the human body are composed of tissues, the chief of which are: (1) Bony or osseous tissue, (2) fibrous or connective tissue, (3) muscular or contractile tissue, (4) nervous or conductile tissue. These tissues are formed by a collection of cells. A cell is a soft, jelly-like substance called protoplasm (living matter), the chemical constituents of which are three gases—hydrogen, nitrogen, oxygen —combined with three solids—carbon, sulphur, and phosphorus.

Each organ of the body is adapted to fulfil some special function ; for instance, the eye is the organ of sight, the stomach an organ of digestion, and so on.

All the tissues are built up and nourished by the blood.

The bony tissue forms THE SKELETON. There are over 200 bones in the human skeleton, which form a strong framework of hard, tough material, which protects internal soft parts, supports the limbs and trunk, and gives attachment to muscles. The hardness of bone is due to calcareous or earthy matter, and the toughness to an animal substance resembling cartilage. Bones are of different shapes ; there are long, short, flat, and irregular bones. The two first are in the limbs ; the two last, with the exception of the patella and scapula, are in the trunk and head. The bones of the head and trunk form cavities for and protect the organs contained in them.

Fig. 9.—Skeleton, Front View.

1. Cranium; 2. cervical vertebrae ; 3 to 3. ribs; 4. clavicle; 5. scapula; 6. humerus; 7. radius; 8. ulna; 9. bones of carpus; 10. bones of metacarpus; 11. phalanges; 12. femur; 13. patella; 14. tibia; 15. fibula; 16. bones of tarsus; 17. bones of metatarsus ; 18. phalanges ; 19. pubes

Fig. 10.—Skeleton, Back View.

1, Cranium ; 2, cervical vertebras ; 3 to 3, dorsal vertebrae ; 4, scapula ; 5, lumbar vertebrae ; 6, ilium ; 7, sacrum ; 8, coccyx ; 9, ischium.

The long bones consist of two ends and a shaft ; in the shaft there are two forms of bony tissue, a compact, and a spongy. The compact is on the surface, and the spongy within it; there is a canal in the centre called the medullary canal, which contains marrow. There are openings in the compact bone for bloodvessels, lymphatics, and nerves, which are called Haversian canals, from Havers, who discovered them. The fibrous membrane covering bone is called periosteum ; small vessels from it pierce the bone underneath and supply it with blood. The ends of bone consist mainly of spongy or cancellated bony tissue covered by cartilage. The marrow in the ends of long bones and in all short and flat bones is red ; it contains many bloodvessels and little fat. In the shafts of long bones the marrow is yellow ; it consists chiefly of fat, and has also bloodvessels.