Structure of the skeleton

Pectoral girdle:

The pectoral or shoulder girdle is firmly fused (joined bone to bone) to the upper bony plates and to the lower front plastron bones. The muscles for swimming are enlarged and the pectoral bones (including the elongated coracoid and scapula ) provide a large surface area for muscle attachment. In most 4 legged vertebrates (animals with backbones), the pectoral girdle is attached to the ribs by muscle which allows for flexibility when the animal lands on its front legs.