Describe the circumstances that reunite Buck and his wild brother?

After Thorton's death, Buck sits and contemplates the ache in his heart. He feels a bit better only when he looks at the bodies of the men he has killed. He realizes that men are no match for dogs without their arrows, clubs and spears.

That night Buck hears the call once more, and this time he knows he must leave for good. Nothing remains to hold him. The wolf pack rushes into the clearing, but they come to a halt upon seeing Buck. The boldest one strikes Buck and instantly has his neck broken. The rest descend, but Buck holds them off for half an hour. The wolves draw back, discomfited. One steps forward and whines softly. Buck recognizes his wild brother, and they touch noses. When the pack howls, Buck joins them. Obeying the law of club and fang, they accept his fellowship, and he runs with them into the woods.