Shoulder girdle
When the shoulder girdle - lat. Cingulate membri superioris (human, literally "belt of upper limb") and cingulate membri thoracici (animals, "Belt of chest-limb") - is known in vertebrates , the bones , the forelimbs (in humans connect the upper arms, i.e. the arms, to the trunk. Together with the pelvic girdle , the shoulder girdle belongs to the so-called zonoskeleton .
There are essentially three bones that are not formed in the same way in all vertebrates:
- Shoulder blade (scapula)
- Collarbone (clavicle)
- Raven leg (coracoid)
In bony fish , the shoulder blade and raven bone are connected in a U-shape. The collarbone is already indicated as a skin ossification. The amphibians have no collarbone. In reptiles , the collarbone and shoulder blade are often only cartilaginous , and there is also an interclavicle that connects the actual collarbone with the breastbone ( sternum ). Even in reptiles without extremities (such as snakes ), remnants of the collarbone and shoulder blade are still present. Birds have all three bones of the shoulder girdle. The raven leg is the strongest bone in them (→ bird skeleton ).
In most mammals (including humans ) the raven bone has receded into an extension ( coracoid process ) on the shoulder blade. Only the monotons have an independent raven leg. The collarbone is also regressed in most mammals, but it is present in humans and is articulately connected to the manubrium sterni (part of the sternum ). With the exception of humans and primates, the most important or even the only bone to connect to the trunk is the shoulder blade, which is muscularly connected to the chest ( synsarcosis ).