Anatomy means really the study of the body, its different parts and their functions, comprising histology, physiology, and many other sciences; but the generally accepted definition is, that the science of anatomy is the study of the body as far as it can be done by dissection and the naked eye. It is necessary, therefore, to have certain well-defined terms for the purposes of description; it is always assumed that the body is in the erect position with the arms by the sides, the palms turned forwards and the thumbs outward.

Sections are generally taken through the three following planes :

1. Transverse, or horizontal plane.

2. Sagittal - a vertical plane in the antero-posterior direction.

3. Frontal - a vertical plane at right angles to the sagittal.

The Mesial Plane is the sagittal one that divides the body in two halves, and is represented in front by the anterior median line, and behind by the posterior median line: the two halves are supposed to be symmetrical; but like all things of Nature's manufacture, are not rigidly so. Certain unpaired organs, that are not in the middle line, also render the two . halves asymmetrical.

The terms internal and external are used to express positions nearer to, or farther from, the middle line respectively; the terms dorsal and ventral are positions nearer the back or front of the body respectively; posterior and anterior are synonymous with dorsal and ventral; superior and inferior indicate nearer the head or the feet respectively. In the case of the limbs, the terms proximal and distal are used to indicate positions near to or distant from the trunk.

The body consists of a bony framework, the component parts of which are jointed together, the joints being the fulcrums of the levers formed by the muscles. As well as the skeletal and muscular systems, the circulatory, respiratory, digestive, and nervous systems also have to be studied.

The Skeletal System

The bones are classed as long, short, flat, or irregular, according to their shape. They are all laid down in cartilage in the embryo, and become ossified at different stages. Various centres of ossification are laid down in different parts of the bone, so that each part can continue growing until the adult size is reached, by which time the different centres of ossification have coalesced and the bone is completely ossified. A sesamoid bone is one that is developed in a tendon passing over a joint where there is a great deal of friction.

Joints are formed by the ends of two bones in apposition to one another. Fibrous bands, called "ligaments," hold them together, and these generally join one another so as to form a complete capsule round the joint. The opposed ends of the bones are covered with cartilage of a particularly tough kind to prevent wear by friction. In some cases where the joint has constant work-e.g., the knee-joint-an extra piece of cartilage in the form of a disc is found between the bones. The whole structure is lined by synovial membrane-a thin membrane which secretes a fluid for the purpose of lubrication.

The skeleton consists of a vertebral column which supports the trunk, and on the top of which is the head, on the freely movable cervical vertebrae; the lower end of the vertebral column is firmly welded together to support the weight of the body. The upper half of the body-the thorax-is protected by a bony framework formed by the ribs, which are elastic and freely movable, to give free play to the lungs. The lower half of the trunk, the abdomen, has only partial bony protection and a strong muscular wall composed of three layers of muscles with the fibres arranged in different directions, so that they can exert strong contractile force.

The limbs are similiar in structure as to the number and arrangement of their bones and joints; but in every particular it will be noticed that the upper limb is constructed with a view to wide scope of movement and lightness, whereas the construction of the lower limb tends to stability and weight. They are each attached by a ball-and-socket joint to a bony girdle. But compare the shoulder girdle with the pelvic : the socket in the one case is shallow and much smaller than the ball; in the other the ball is received into a deep socket that covers it up to the neck. The shoulder-girdle is connected anteriorly to the trunk by a loose gliding joint, and posteriorly slung by muscles. The pelvic girdle is firmly welded together in front, and behind is almost immovably joined to the lower vertebrae, whose joints are completely ossified. The reason for this is easily seen when the functions of the upper and lower limbs are compared.