dimly, dazed by the searing pain in his arm, he slid sideways on his rain-drenched broom, one knee still crooked over it,

中国大学MOOC: "Dimly, dazed by the searing pain in his arm, he slid sideways on his rain-drenched broom, one knee still crooked over it, his right arm dangling useless at his side." (Harry Porter)This sentence is a _____________.