Final answer:
The midpoint position at the junction between the proximal end of the clavicle and the sternum is known as the sternoclavicular joint, which is critical for shoulder mobility.
Step-by-step explanation:
The midpoint position of the palpable junction between the proximal end of the clavicle and the sternum at the upper border (jugular notch) of the sternum is called the sternoclavicular joint. This joint is significant as it forms the only bony attachment between the pectoral girdle of the upper limb and the axial skeleton, allowing considerable mobility for shoulder movements. The nearby jugular notch is a shallow, U-shaped border at the top of the manubrium, which can be easily felt at the base of the neck between the medial ends of the clavicles.