Okay, let's tackle this question about the brachiocephalic vein. The question is asking which statement is NOT true about the brachiocephalic vein. First, I need to recall the anatomy of the brachiocephalic veins. There are two of them: the left and right. They are formed by the union of the internal jugular and subclavian veins.

The right brachiocephalic vein is shorter because it has to cross over to the left to join the left brachiocephalic vein and form the superior vena cava. The left one is longer since it doesn't have to cross. So any statement claiming the right is longer would be incorrect.

Also, the brachiocephalic veins drain into the superior vena cava, not the inferior. So if an option says they drain into the inferior vena cava, that's wrong. Another point is the location of the thoracic duct. The right brachiocephalic vein lies anterior to the right subclavian artery, while the left is posterior to the left subclavian artery. So if an option states the opposite, that's incorrect.

The brachiocephalic veins are located in the superior mediastinum, so any mention of the posterior mediastinum would be wrong. Also, the right brachiocephalic vein is formed at the level of the first rib, while the left is formed slightly higher. If an option says they are formed at the same level, that's incorrect.

Now, looking at the options. Let's assume the options are something like:

A. Formed by union of internal jugular and subclavian veins
B. Right brachiocephalic vein is longer than the left
C. Drains into inferior vena cava
D. Lies anterior to subclavian artery on the right

If B is the correct answer (the incorrect statement), then the explanation would be that the right brachiocephalic vein is actually shorter because it has to cross over. The correct answer is B. The other options: A is correct because that's how they form. C is incorrect but if it's an option, then it's wrong. D is correct because the right vein is anterior to the subclavian artery. So the answer is B.

**Core Concept**
The brachiocephalic veins are formed by the union of the internal jugular and subclavian veins. The right brachiocephalic vein is shorter than the left due to its course crossing the midline to join the left brachiocephalic vein and form the superior vena cava.

**Why the Correct Answer is Right**
The **right brachiocephalic vein** is shorter than the left because it must cross the midline to drain into the left brachiocephalic vein, which then forms the superior vena cava. The left brachiocephalic vein does not cross the midline, making it longer. This anatomical asymmetry is critical for venous return from the upper body.

**Why Each Wrong Option is Incorrect**
**Option A:** *If it claimed the brachiocephalic vein is formed by the external jugular and subclavian veins*—incorrect, as the internal jugular, not external, combines with the subclavian.
**Option C:** *

✓ Correct Answer: D. Right vein unite at 1st costal cailage