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Dog Body Structure
Each species differs from the next in form; breeds within speciesdiffer from other breeds, and individual dog vary in some respects.The skeleton on which the soft tissue of the body hangs is the basiccause of these structural differences. In some dog, for example, themere shortness of certain leg bones can cause a startling difference inappearance contrast the Basset Hound with the Foxhound, the two breeds arc alike in all major respects except leg length. The skeleton is a marvelous framework replete with strength wherestrength is needed, rigidity where rigidity is needed, flexibility, swivels,and hinges where stretching, bending, and rotating are required. Somebones are solid, others are hollow or filled with marrow in which redblood cells may be generated. Some are mere beads and others long andstrong. The way they are joined is an interesting study in itself. Thereare ball-and-socket joints (hips), hinge joints (knees), others made byone bone abutting on another with a cushion between (vertebrae), andmodifications of all three kinds. Some dog arc more agile thanothers; some have difficulty turning around in a short radius, whereasothers, because of their skeletal construction, can "turn on a dime." Each long bone is made up of a shaft of hard, brittle material with asoft center of marrow and has ends of spongy material with a coveringof dense, hard bone. Around the whole bone is a sort of skin called theperiosteum. On top or on the bottom of the spongy end if the boneterminates at a joint is a springy, cartilaginous pad which takes theshocks. All through the bone small spaces form tunnels that carry bloodand nerves; nourishment is also furnished by the periosteum. Some bones are flat: ribs, head bones, and shoulder blades are examples. They are not as solid as they seem but arc well fortified withnourishment. The ribs join at the lower extremities with cartilages.These look like true ribs but are only extensions upward from a flat"bone" the sternum, or breastbone to which all but one or two ofthe last ribs in some species are joined. The sternum is not actually abone but is composed of springy, tough cartilage. The breastbone needsto be flexible, considering the strain it undergoes. Muscles. Skeletal muscles help hold the framework together, cooper-ate with it in locomotion, and are easily detected beneath the skin.There arc two kinds of muscles: the skeletal and the others, not visibleoutside of the body, called the smooth muscles. When seen under amicroscope, fibers of a skeletal muscle appear to have bands or stripes that do not exist on the smooth muscles. The striated muscles areunder voluntary control. The duties of the smooth muscles are gener-ally restricted to the functioning of organs and the digestive tract. Thegullet, intestines, bladder, blood vessels, and sphincter muscles, whichact more or less involuntarily, are all smooth.
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The skeleton serves as the framework of the body andprovides protection for the organs. The ribs cover the lungs, heart,liver, stomach, kidneys, and pancreas; the skull covers the brain and such delicate organs as the hearing mechanism and the organs of scent.