蹲う (Tsukubau) means bowing to the ground and 踞む (Kogomu) means bending down, sitting down or crouching, and therefore the combination of these two characters can represent the posture of bowing politely with one's body bended down that is taken to show respect toward any person of high rank passing by.
蹲う（つくばう）には平伏・平身低頭する意味、踞む（こごむ）は屈み込んだ状態を指し、腰をかけたり中腰の状態の踞ぐ（しりうたぐ）を指すことから転じて貴人が通行する際にしゃがんだ状態で礼をするさまを言う。