Mankind, they said, sprang out of a large cane with two joints, that, floating about in the water, was at length thrown by the waves against the feet of the glede as it stood on shore, which opened it with its bill; the man came out of one joint, the woman out of the other.

Formation of Joints.

The various bones of the skeleton are connected together at different parts of their surfaces by joints, or articulations.

Many different kinds of joints have been described, but the same general plan obtains for nearly all.

Bones make the chief element of all the joints, and their adjoining surfaces are shaped to meet the special demands of each joint (Fig. 27).

A very delicate connective tissue, called the synovial membrane, lines the capsules of the joints, and covers the ligaments connected with them.

It secretes the synovia, or joint oil, a thick and glairy fluid, like the white of a raw egg, which thoroughly lubricates the inner surfaces of the joints.

It is only perfect joints that are fully equipped with the structures just mentioned.

Such joints allow little or no motion and have no smooth cartilages at their edges.

Thus, the bones of the skull are dovetailed by joints called sutures, which are immovable.

The union between the vertebræ affords a good example of imperfect joints which are partially movable.

26.Elastic Tissue from the Ligaments about Joints.

Perfect Joints.

They an divided into hinge joints, ball-and-socket joints and pivot joints.

They an divided into hinge joints, ball-and-socket joints and pivot joints.

The hinge joints allow forward and backward movements like a hinge.

These joints are the most numerous in the body, as the elbow, the ankle, and the knee joints.

These joints are the most numerous in the body, as the elbow, the ankle, and the knee joints.

These joints permit free motion in almost every direction.

In many joints the extent of motion amounts to only a slight gliding between the ends of the bones.

Tendons are most numerous about the larger joints, where they permit free action and yet occupy but little space.

The muscles supply the power for moving the bones, and the joints act as fulcrums or points of support.

A line dropped from this point would fall between the feet, just in front of the ankle joints.

Now, on account of the large number and flexibility of the joints, the body could not be kept in an upright position without the cooperation of certain groups of muscles.

After long confinement to the bed from disease, the joints have wasted ligaments, thin cartilages, and the bones are of smaller proportions.