BIOLOGY Volume 2 - A Guide to General Biology - 2004
18. THE ANIMAL SKELETOMUSCULAR SYSTEM
18.3. Anatomical Structure of the Mammalian Skeleton (Using the Rabbit as an Example)
18.3.4. Joints
In vertebrates with a bony Skeleton, joints are formed at the sites where bones connect. Movement of adjacent skeletal elements relative to one another is possible only when joints are present between them. Mammalian skeletal joints are highly diverse, as summarized in Table 18.2.
Class="center">Table 18.2. Diversity of joints in the mammalian endoskeleton
Joint type |
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Fixed (synarthrosis) |
A thin layer of Fibrous Connective Tissue or Cartilage lies between the bones, rigidly fixing their position |
Between Skull bones; between the sacrum and the ilium of the Pelvic Girdle; between the BONES OF THE pelvic girdle |
Provides body support; imparts strength or protects delicate Organs that cannot tolerate any kind of deformation |
Slightly movable (amphiarthrosis) |
Bones are separated from each other by cartilaginous pads |
||
a) Gliding |
Between vertebrae; carpal and Tarsal Bones |
Bones glide relative to each other, but their mobility is limited. Together they provide a variety of movements and impart strength to the limb |
|
b) Pivot (cylindrical) |
Between the atlas and axis |
Allows HEAD rotation |
|
Movable (synovial, diarthrosis; Fig. 18.14) |
The articulating surfaces of the bones are covered with cartilage and separated by a synovial cavity filled with synovial fluid |
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a) Hinge |
A relatively small number of Muscles are involved in the movement |
Knee and elbow joints, finger joints |
Allows movement in a single plane around a single axis. Can withstand heavy loads |
b) Ball-and-socket |
Numerous muscles are attached to the bones forming the joint |
Shoulder and hip joints |
Allows movement in all planes and some rotation. Not capable of withstanding very heavy loads |
True joints (diarthroses) share a similar "design." The articulating surfaces at the ends of the bones are covered with smooth hyaline cartilage. Although cartilage is living tissue, it lacks nerves and Blood Vessels. The nutrients and oxygen it requires diffuse through the synovial membrane and synovial fluid. During movement, cartilage reduces friction between the bones; thanks to its elasticity, it also acts as a Shock absorber upon impact. The ligaments surrounding the joint form a dense fibrous capsule and hold the bones in a specific position. The ligaments are attached to both bones and arranged in such a way that the joint can withstand the loads placed upon it. The inner cavity of the Joint Capsule is lined with a synovial membrane, which secretes synovial fluid into this cavity (Fig. 18.14). This fluid contains mucin and serves as a lubricant for the articular surfaces, reducing friction between them. The synovial membrane acts as a waterproof barrier preventing the loss of synovial fluid. Thus, a joint is effectively a self-sustaining system.
Fig. 18.14. Mammalian diarthrosis (true joint).
Last update: 06/08/2026
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