The limbs
 All bones are connected by joints. We can identify a macro category of joints: synarthroses and diathroses.
Synarthroses are immobile or semi-mobile joints, with little or no space between the connected bones, which are joined by means of cartilaginous or fibrous tissue.
Diathroses are adequately mobile, foresee contact between the bone heads by means of encrusted cartilage and their stability is guaranteed by ligamentous complexes and articular capsules.
The articular capsule stabilizes articulation and is rich in synovial liquid on the inside, which lubricates and nourishes the cartilage.
The articulations fundamentally have:
- ligaments: they provide reinforcement and conduction. They enable giving further stability and transmit movement. In some cases there are also ligaments that limit articular range (ex. The crossed ligaments in the knee);
- articular bursae and sheaths;
- disks and meniscs: inserted between the bone heads, they optimize contact between the heads and absorb part of the trauma bones are subjected to;
- articular lips: they consist of fibrous connective tissue and their task is to virtually increase the articular cavity.
Articulations can permit a more or less wide range of motion and connect two or more articular heads. In the first case they are defined as simple and in the second compound.
In virtue of the mobility permitted by the diathroses and the anatomical conformation of the articular heads, articulations can be divided into the following types:
- pivot: typical joints in flat articular surfaces (ex.: the vertebrae), they enable bones to slide and rotate together, normally within a reduced range;
- hinge: these joints enable motion of flexion-extension (angular ginglymus, ex.: humerus-ulna articulation) or rotation (lateral ginglymus, ex.: radius-ulna articulation), they can be distinguished between concave and convex articular surfaces;
- saddle: they also consist of the moulding of concave and convex articular surfaces, with a double curvature similar to the shape of a saddle (ex.: carpal-metacarpal joints);
- ball and socket: they are formed by a convex bone penetrating a concave on. They permit a good deal of motion. (ex. hip-femur, shoulder joints);
- condyloid: it has characteristics similar to trochlear articulation and can be found on elliptical surfaces (ex.: wrist articulation);
The synathroses (articulations that permit a great deal of movement) can be classified in: syndesmoses (the connection is formed by collagen fiber); syncondroses (joined by hyaline cartilage); synphises (connected by fibrous cartilage and connective tissue); synostoses (a bony joint, fruit of the moulding of bone surfaces as a consequence of growth).
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