下鼓室乃鼓室在外耳道底平面以下之部分,其底稍呈半球形,凹面向下。底壁属岩部的组成部分,窄而斜向前并稍向下,将鼓室与下方的颈静脉圆顶相分隔。该壁可厚可薄,新生儿者即为薄壁(有时缺损),随生长发育而渐增厚,其增厚程度视颈静脉球的发育而定。若颈静脉球突向下鼓室,底壁就很薄,甚至缺损,反之则很厚。通常自内向外有骨性小梁覆盖,致下壁不规则,可能遮蔽其凸状外观。在鼓室外壁与下壁交界处有鼓室下隐窝,其后界为茎突复合体(styloid complex),前界 Under the tympanum tympanic room in the bottom of the outer ear canal part of the plane, the bottom slightly hemispherical, concave down. The bottom wall is a component of the rock, narrow and oblique forward and slightly downward, separating the tympanic dome from the jugular dome below. The wall can be thick and thin, neonatal thin-walled (sometimes defect), with growth and gradually thickening, the thickening of the development of the jugular bulb depending on. If the jugular bulb down to the tympanic cavity, the bottom wall is very thin, or even defect, and vice versa is very thick. Bone trabecular bone is usually covered from the inside out, resulting in an irregular inferior wall that may mask its convex appearance. Under the tympanic wall and the lower wall at the junction of tympanic recess, the latter sector styloid complex (styloid complex), the frontier