The sternum of the horse is shaped somewhat like a canoe; it is
compressed laterally, except in its posterior part, which is flattened
dorso-ventrally. It is inclined obliquely so that the posterior end is
about six to eight inches (15 to 20 cm.) lower than the anterior.
The =dorsal surface= has the form of a very narrow isosceles triangle
with the apex in front. It is concave longitudinally, flattened
transversely.
The =lateral surfaces= are convex above, slightly concave below, and
diminish in extent behind. Each presents on its upper part seven
=articular cavities= (Foveæ costales), which receive the sternal ends of
the second to the eighth costal cartilages inclusive. These cavities are
situated in series at the intersternebral junctions. The first four are
elliptical in outline with the long diameter vertical, and are separated
by considerable regular intervals. The others are progressively smaller,
more circular, and closer together. The area below these cavities gives
attachment to the pectoral muscles.
[Illustration: