请教老师：On they struggled, fighting, dying, marking every step of the route with their dead. 这个句子的主谓宾等语法结构分别是什么？关联的语法点叫什么？

上下文：

It was but a small body of survivors that at length escaped from that deadly defile and threw up entrenchments for the night in a more open spot. With the dawn of the next day they resumed their progress, and were at no great distance from their stronghold of Aliso when they found their progress arrested by fresh tribes, who assailed them with murderous fury. On they struggled, fighting, dying, marking every step of the route with their dead.