8. (10 points) Please fill in each arrow with an appropriate number, so that the number in the arrow indicates how many different numbers are in the direction the arrow points. Then, the four-digit number formed by the numbers filled in from left to right in the second row of the figure is (the figure below is an example of a $3 \times 3$ grid).


Fill in the appropriate numbers in each arrow in the figure below, so that the number in the arrow indicates how many different numbers are in the direction the arrow points. Then, the four-digit number formed by the numbers filled in from left to right in the second row of the figure is (the figure below is an example of a $3 \times 3$ grid).
【Answer】Solution: According to the analysis, start deducing from the first of the second row, so the first should be 1;
The second points to the two spaces on the right, which can only be 1 or 2,
If it is 1, because the third points to one number on the right, it can only be 1, so the fourth arrow can only be 1, and the fourth arrow points to two numbers below,

If it is 1, then the fourth arrow in the third row can only be 3, but the fourth in the third row points to two numbers above, it cannot be 3, so there is a contradiction, so the second arrow can only be 2;

The third in the second row points to the right, and there is only one number on the right, so it can only be 1;
And the fourth in the second row points to two numbers below, and the second arrow indicates that the fourth number is different from the third number, so the fourth number can only be 2.

Therefore, the numbers to be filled in the second row are: 1212,
As shown in the figure:
So these four numbers are: 1212,
The answer is: 1212.