Anatomy of the (human) chest
It is important to realize that the shape of
the chest does not correspond to that of the bony thorax
which encloses the heart and lungs; all the breadth of the
shoulders is due to the shoulder girdle, and contains the
axilla and the head of the humerus. In the middle line the
suprasternal notch is seen above, while about three fingers'
breadth below it a transverse ridge can be felt, which is
known as Ludovic's angle and marks the junction between the
manubrium and gladiolus of the sternum. Level with this line
the second ribs join the sternum, and when these are found
the lower ribs may be easily counted in a moderately thin
subject. At the lower part of the sternum, where the seventh
or last true ribs join it, the ensiform cartilage begins,
and over this there is often a depression popularly known as
the pit of the stomach. The nipple in the male is situated
in front of the fourth rib or a little below; vertically it
lies a little external to a line drawn down from the middle of
the clavicle; in the female it is not so constant. A little
below it the lower limit of the great pectoral muscle is seen
running upward and outward to the axilla; in the female this
is obscured by the breast, which extends from the second to
the sixth rib vertically and from the edge of the sternum
to the mid-axillary line laterally. The female nipple is
surrounded for half an inch by a more or less pigmented disc,
the areola. The apex of a normal heart is in the fifth left
intercostal space, three and a half inches from the mid-line.
- (from an old encyclopedia)