e process of upper jawbone;
B, zygoma, forming zygomatic arch;
C, condyle for forming articulation with atlas;
D, foramen magnum;
E, occipital bone.
]

The longest bone in the face is the inferior maxillary, or lower jaw.
It has a horseshoe shape, and supports the lower set of teeth. It is the
only movable bone of the head, having a vertical and lateral motion by
means of a hinge joint with a part of the temporal bone.

35. Sutures of the Skull. Before leaving the head we must notice the
peculiar and admirable manner in which the edges of the bones of the outer
shell of the skull are joined together. These edges of the bones resemble
the teeth of a saw. In adult life these tooth-like edges fit into each
other and grow together, suggesting the dovetailed joints used by the
cabinet-maker. When united these serrated edges look almost as if sewed
together; hence their name, sutures. This manner of union gives unity
and strength to the skull.

In infants, the corners of the parietal bones do not yet meet, and the
throbbing of the brain may be seen and felt under these "soft spots," or
_fontanelles_, as they are called. Hence a slight blow to a babe's head
may cause serious injury to the brain (Fig. 14).

The Bones of the Trunk.

36. The Trunk. The trunk is that central part of the body which
supports the head and the upper pair of limbs. It divides itself into an
upper cavity, the thorax, or chest; and a lower cavity, the
abdomen. These two cavities are separated by a movable, muscular
partition called the diaphragm, or midriff (Figs. 9 and 49).

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 Vertebrae.
12 Dorsal Vertebrae.
5 Lumbar Vertebrae.
1 Sacrum.
1 Coccyx.

II. Ribs, 24 bones:
14 True Rib