The bones of the trunk are variously related to each other, and some of
them become united during adult life into bony masses which at earlier
periods are quite distinct. For example, the sacrum is in early life made
up of five distinct bones which later unite into one.

The upper cavity, or chest, is a bony enclosure formed by the
breastbone, the ribs, and the spine. It contains the heart and the lungs
(Fig. 86).

The lower cavity, or abdomen, holds the stomach, liver, intestines,
spleen, kidneys, and some other organs (Fig. 59).

The bones of the trunk may be subdivided into those of the spine, the
ribs, and the hips.

The trunk includes 54 bones usually thus arranged:

I. Spinal Column, 26 bones:
7 Cervical Vertebræ.
12 Dorsal Vertebræ.
5 Lumbar Vertebræ.
1 Sacrum.
1 Coccyx.

II. Ribs, 24 bones:
14 True Ribs.
6 False Ribs.
4 Floating Ribs.