The cranium is a curved bone which surrounds the brain.
Sesamoid bones, for example the patella, develop within the tendons of skeletal muscle.
Joints can be classified according to the type of material holding the bones together, the relative mobility of the joint or the degrees of freedom of the joint.
In a synoteosis the bones are fused together, for example in the cranium. These joints are non-mobile.
In a synchondrosis the bones are held together by cartilage, for example the joint between the first rib and the sternum. These joints are non-mobile.
In a syndesmosis the bones are held together by Fibrous Connective Tissue (FCT), for example the joint between the tibia and the fibula. These joints are semi-mobile.
Synovial articulations are mobile to various degrees, they can be uniaxial, biaxial or multiaxial.
Joints can be ball and socket (for example the hip joint), hinge (for example the knee joint) or specialised (for example the pivot-type joint for rotation of the head).