sentences:  Colquhoun pushed on his force to get through the glen before encountering with the MacGregors, but they were already aware of his approach and Allaster MacGregor pushed forward one of his divisions and entered the head of the glen in time, to prevent the Colquhouns from emerging out of the upper end of the glen.Meanwhile, his brother, John MacGregor, with the ambush division took a detour to the rear of the Colquhouns which prevented their retreat back through the glen without fighting their way through.The Colquhouns also least expected to be attacked from the rear.