The Muscular System

The flesh of the body consists of a number of muscles which are attached at each end to bones. They are capable of contraction, the attachment from which they pull being termed the "origin," and the one on which they pull, the "insertion." A muscle or its tendon passes over one or more joints, and its principal action is on the joint nearest the insertion.

The Circulatory System

The tissues are nourished by the blood, which is carried to all parts by the arteries and returned by the veins. The heart is the starting-point of the system, and by its action the blood is sent on its way at a certain pressure.

The Respiratory System consists of an air passage from the mouth and nose to the lungs, the latter situated in the thorax, where the blood is reoxygenated.

The Digestive System consists of the alimentary canal, by which food is taken in at the mouth, passed down to the stomach and duodenum to be digested, into the small intestine to be absorbed, and the residue into the large intestine to be excreted. Accessories to the digestive system are the organs which secrete digestive juices and pour them into the alimentary canal.

The Nervous System is in two parts-the cerebro-spinal and sympathetic. The cerebro-spinal, consisting of the brain and spinal cord, is formed largely of grey matter, which consists of the actual nerve cells, and sends distributing fibres in every direction, so that each muscle receives both an efferent and afferent branch. The sympathetic is an accessory system.

The whole body is covered by a thin tough membrane called the "deep fascia," which closely invests the muscles, and sends down processes, or dividing septa, between them. From the deep fascia and the intermuscular septa many of the muscles get additional origins, and in some cases muscles are inserted into adjacent fascia as well as bones. Outside this is the superficial fascia, a thin friable membrane enclosing fat in its meshes. This fascia is also found in spaces between muscles, bones, and organs to prevent jarring and give elasticity. Over all is the skin, from which the hair and nails are developed.