Which vein does the axillary vein convert into as it courses toward the heart?

The axillary vein transitions into the subclavian vein as it travels toward the heart. This conversion happens at the lateral border of the first rib. The axillary vein is formed by the merging of the brachial and basilic veins in the axilla, and it continues to join the subclavian vein, which then ultimately contributes to the formation of the brachiocephalic vein. The anatomical flow from the axillary to the subclavian vein is important for understanding the venous drainage of the upper limb and the thorax.

Each of the incorrect options refers to veins that are either tributaries or located in different regions without a direct sequential relationship to the axillary vein's course toward the heart. The basilic vein, while it does contribute to the axillary vein, does not represent the transition at the point of interest, and the radial vein is a branch located in the forearm, which does not directly relate to the route taken by the axillary vein. The cephalic vein also does not transition from the axillary vein but instead runs more laterally and drains into the axillary region without being a continuation into the subclavian.