4-23. SYNOVIAL MEMBRANE, FLUID, AND CAVITY
The inner surface of this fibrous capsule is lined with a synovial membrane. The
synovial membrane secretes a synovial fluid into the synovial cavity, or joint space. The
synovial fluid is a very good lubricant. Thus, it minimizes the frictional forces between
the moving bones.
The bones of the synovial joint are held together by ligaments. Ligaments are
very dense FCT structures that keep the bones from being pulled apart. These
ligaments may occur as either discrete, individual structures or as thickenings of the
4-25. SKELETAL MUSCLES
The skeletal muscles cross the synovial joint from one bone to the other. They
are attached to the bones. The tonic (continuous) contraction of these skeletal muscles
holds the opposing surfaces of the bones tightly together. When properly stimulated,
these muscles contract and cause motion of the bones around the joint.
4-26. TYPES OF SYNOVIAL JOINTS
Synovial joints are often referred to by their geometric or mechanical structure.
a. Ball-and-Socket Joint. The ball-and-socket synovial joint has one bone with
a rounded head, a "ball." The other bone has a corresponding cavity, the "socket." The
ball-and-socket joint is usually multiaxial.
b. Hinge Joint. In the hinge joint, the geometry of the bony surfaces and the
disposition of the ligaments are such as to allow the parts to fold on each other, around
a single axis only.
c. Others. There are other special arrangements of the synovial joints to
produce specific motions. An example: Rotation of the head at the pivot-type joint of
atlas and axis (the upper two vertebrae).
Section IX. THE AXIAL SKELETON
4-27. INTRODUCTION TO THE HUMAN SKELETON
As a whole, the human skeleton (Figure 4-4) is the supporting framework of the
body. The skeleton is composed of the individual bones and the articulations