In anatomy, a joint capsule or articular capsule is an envelope surrounding a synovial joint.
Each joint capsule has two parts: an outer fibrous layer or membrane, and an inner synovial layer or membrane.
An outer (fibrous membrane, fibrous stratum) composed of avascular white fibrous tissue.
An inner (synovial membrane, synovial stratum) which is a secreting layer
On the inside of the capsule, articular cartilage covers the end surfaces of the bones that articulate within that joint.
The outer layer is highly innervated by the same nerves which perforate through the adjacent muscles associated with the joint.
The fibrous membrane of the joint capsule is attached to the whole circumference of the articular end of each bone entering into the joint, and thus entirely surrounds the articulation. It is made up of dense irregular connective tissue. It's a long spongy tissue.