pelvis. These four bones are the sacrum and the coccyx,
which have been described, and the two hip bones.

[Illustration: Fig. 17.--Thorax. (Anterior view.)]

The hip bones are large, irregularly shaped bones, very firm and
strong, and are sometimes called the haunch bones or _ossa innominata_
(nameless bones). They are united to the sacrum behind and joined to each
other in front. On the outer side of each hip bone is a deep cup, or
socket, called the _acetabulum_, resembling an ancient vinegar cup, into
which fits the rounded head of the thigh bone. The bones of the pelvis are
supported like a bridge on the legs as pillars, and they in turn contain
the internal organs in the lower part of the trunk.

41. The Hyoid Bone. Under the lower jaw is a little horseshoe shaped bone
called the hyoid bone, because it is shaped like the Greek letter upsilon
([Greek: u]). The root of the tongue is fastened to its bend, and the
larynx is hung from it as from a hook. When the neck is in its natural
position this bone can be plainly felt on a level with the lower jaw and
about one inch and a half behind it. It serves to keep open the top of the
larynx and for the attachment of the muscles, which move the tongue. (See
Fig. 46.) The hyoid bone, like the knee-pan, is not connected with any
other bone.



The Bones of the Upper Limbs.


42. The Upper Limbs. Each of the upper limbs consist of the upper