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CHAPTER VIII. 
Plate X. — the chest, patella, and shoulder-blade. 
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 con¬ 
cave 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 “ un 
like 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 constant¬ 
ly, under the corresponding joints of the other toes. The sesamoid 
bones, like the patella, remove their tendons from the centre of mo¬ 
tion, facilitate their glidings over the bone, and protect their artic¬ 
ulations. 
Fig. 4. The shoulder-blade ( scapula ) is joined to the collar bone 
by ligaments, and to the thorax by powerful muscles which are ca¬ 
pable 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. 
