Body Organs

The lung is an organ of the Respiratory System of air-breathing vertebrates and some fishes and amphibians that takes in atmospheric oxygen, needed for energy production, and at the same time expires carbon dioxide, a waste product of this metabolism. The lungs of most animals consists of two elastic chambers, usually located in the thorax, with thin linings across which oxygen and carbon dioxide are exchanged between blood capillaries and the air within the chamber. In evolutionary term, lungs are the counterparts of the gills of fish and crustaceans, which are adapted for extracting oxygen from water, and the tracheae of insects, which pipe oxygen directly to the tissues. The development of the lungs permitted the eventual evolution of oxygen, which can be extracted more quickly from air than from water.

The principal salivary glands communicating with the mouth and pouring their secretion into its cavity are the parotid, submaxillary, and sublingual. The parotic gland, so called from being placed near the ear is the largest of the three salivary glands, varying in weight from half an ounce to an ounce. It lies upon the side of the face immediately below by the angle of the jaw and by a line drawn between it and the mastoid process: anteriorly, it extends to a variable extent over the Masseter muscle; posteriorly it is bounded by the external meatus, the mastoid process and the Sterno mastoid and Digastric muscles, slightly overlapping the two muscles. Its anterior surface is grooved to embrace the posterior margin of the ramus of the lower jaw, and advances forward beneath the ramus, between the two Pterygoid muscles and superficial to the ramus over the Masseter muscle. Its outer surface, slightly lobulated, is covered by the integument and parotid faseia and has one or two lymphatic