Appendicula Skeleton: Shoulder Gridle 1: Clavicle

The depature of fishes from their aquatic habitat brought profound changes in locomotion. The forelimb gridle ( shoulder gridle), attached to the rear of head, detached and moved tailward, leaving a flexible neck. As this gridle moved back, some of the head's dermal armor and gill muscles remained attached to it, and our own shoulder gridle is still attached to the skull by derivatives of some of these primitive gill muscles. The remaining dermal bone element constitutes part of our clavicle. The human shoulder gridle provides support and articulation for tht humerus and anchors a variety of muscles. The clavicle's function az a strut for the shoulder is made obvious when fracture of this bone is accompanied by anteromedial collaps of the shoulder. The shoulder gridle embraces the Thorax posteriorly, laterallym and anteriorly, providing a platform for movements of the forelimb.

Clavicle

The clavicle forms the anterior portion of the shoulder girdle. It is a long bone, curved somewhat like the italic letter f, and placed nearly horizontally at the upper and anterior part of the thorax, immediately above the first rib.Medially, it articulates with the manubrium of the sternum(breast-bone) at the sternoclavicular joint. At its lateral end it articulates with the acromion of the scapula (shoulder blade) at the acromioclavicular joint.

• It is shorter, thinner, less curved, and smoother in women than in men.

It has a rounded medial end and a flattened lateral end.

The clavicle serves several functions:
It serves as a rigid support from which the scapula and free limb are suspended. This arrangement keeps the upper limb away from the thorax so that the arm has maximum range of movement.
Covers the cervicoaxillary canal (passageway between the neck and arm), through which several important structures pass.
Transmits impacts from the upper limb to the axial skeleton.
Even though it is classified as a long bone, the clavicle has no medullary (bone marrow) cavity like other long bones. It is made up of spongy (cancellous) bone with a shell of compact bone. The clavicle bone is the only bone that does not have marrow. It is a dermal bone derived from elements originally attached to the skull.