bounded anteriorly by the frontal bone, posteriorly by the occipital, and
laterally by the temporal and sphenoid bones. The two bones make a
beautiful arch to aid in the protection of the brain.

The temporal bones, forming the temples on either side, are attached
to the sphenoid bone in front, the parietals above, and the occipital
behind. In each temporal bone is the cavity containing the organs of
hearing. These bones are so called because the hair usually first turns
gray over them.

The occipital bone forms the lower part of the base of the skull, as
well as the back of the head. It is a broad, curved bone, and rests on the
topmost vertebra (atlas) of the backbone; its lower part is pierced by a
large oval opening called the _foramen magnum_, through which the spinal
cord passes from the brain (Fig. 15).

The sphenoid bone is in front of the occipital, forming a part of the
base of the skull. It is wedged between the bones of the face and those of
the cranium, and locks together fourteen different bones. It bears a
remarkable resemblance to a bat with extended wings, and forms a series of
girders to the arches of the cranium.

The ethmoid bone is situated between the bones of the cranium and
those of the face, just at the root of the nose. It forms a part of the
floor of the cranium. It is a delicate, spongy bone, and is so called
because it is perforated with numerous holes like a sieve, through which
the nerves of smell pass from the brain to the nose.

[Illustration: Fig. 14.--The Skull]