Plate 10: The Chest, Patella, and Shoulder-blade
|March 15, 2012||Filled under All text of Paley Natural Theology, Chapter 8||
Fig. 1. The spine, ribs, and sternum, constitute the frame work of the chest or thorax. Referring, however, to the plate, or to nature, we observe that the ribs are not continued throughout from the spine to the sternum, but intervening cartilages complete the form of the chest, by connecting the end of the first ten ribs to the breast bone. This is a farther provision, relative to the mechanical function of the lungs, deserving notice. The muscles of respiration enlarge the capacity of the chest by elevating the ribs; and during the momentary interval of muscular action, the cartilages, from their great elasticity, restore the ribs to their former position.
Fig. 2. Represents the true shape of the patella, the anterior surface convex. Fig. 3, the posterior surface, which has two concave depressions adapted to the condyles of the thigh bone. The projection of the patella, as a lever, or pulley, removes the acting force from the centre of motion, by which means the muscles have a greater advantage in extending the leg. That this bone is “unlike any other in the body,” is a mistake; such bones are numerous, though less obvious, for they do not exceed the size of a pea: these are called sesamoid bones, and are formed in the flexor tendons of the thumb, and sometimes in the fingers. They are frequently found under the tendons of some of the muscles. Two of these sort of bones are constantly found under the articulation of the great toe, with the foot: some also are discovered, though not so constantly, under the corresponding joints of the other toes. The sesamoid bones, like the patella, remove their tendons from the centre of motion, facilitate their glidings over the bone, and protect their articulations.
Fig. 4. The shoulder-blade (scapula) is joined to the collar bone by ligaments, and to the thorax by powerful muscles which are capable of sustaining immense weights, and whose action gives the various directions to the arm, and enables it freely to revolve at the shoulder-joint.
Fig. 5. The os hyoides, a small bone situated at the root of the tongue. It serves as a lever or point for attaching the muscles of the tongue, larynx, and those of deglutition.