(2) In the plane joint, the contact surfaces of the bones are essentially flat.
These flat surfaces slide on one another (also called translatory motion). The
acromioclavicular joint of the shoulder region is an example of a plane joint.
4-11. THE ARTICULAR DISC
In three of the synovial joints of the human body, a special addition is seen. This
addition is known as an articular disc. The joints with articular discs are the temporo-
mandibular joint of the lower jaw, the sternoclavicular joint (at the sternum
(breastbone)), and the ulnocarpal joint of the distal end of the forearm.
a. An articular disc is a fibrocartilage plate. It is inserted between the articular
surfaces of the bones of a synovial joint. In this way, it divides the synovial space into
b. Joints having an articular disc are capable of having several different motions
occurring at the same time. Mechanically, there are really two joints together here.
Section IV. THE HUMAN SKELETON
a. The human skeleton (figures 4-3A and 4-3B) is a collection of individual
bones articulated (joined) together.
b. The major subdivisions of the skeleton are the axial skeleton and the
4-13. THE AXIAL SKELETON
The axial skeleton is the central framework of the human body. It includes the
skull, the vertebral column (spine), and the thoracic cage (chest or rib cage).