Final answer:
The scapula forms an articulation with the thorax at the acromioclavicular joint, which is between the acromion of the scapula and the clavicle's acromial end, enabling upper limb mobility and support.
Step-by-step explanation:
The scapula, or shoulder blade, forms an articulation with the thorax underneath, specifically at the acromioclavicular joint. This joint is the site of articulation between the acromion of the scapula and the acromial end of the clavicle, allowing for movement and support of the upper limb. Additionally, the medial end of the clavicle articulates with the sternum at the sternoclavicular joint, forming the only bony connection between the pectoral girdle and the axial skeleton and providing mobility in multiple directions.