Final answer:
The blank in the classification of joints should be filled with 1) synovial, which is a type of joint with a fluid-filled cavity allowing for increased movement.
Step-by-step explanation:
Joints can be classified structurally as bony, fibrous, cartilaginous, and synovial. The structural classification of joints is based on the type of tissue that binds the bones together, and whether there is a joint cavity present.
Fibrous joints use fibrous connective tissue to hold the bones together tightly, allowing little or no movement. Cartilaginous joints are where the bones are connected by cartilage, providing limited flexibility. Synovial joints are characterized by having a joint cavity filled with fluid, which permits a greater range of movement.