The excellence of latter is that its incision can be adjusted optional . 4 . 17 . 5 % of specimens have angled variation of the back wall of petrous bone 约有17 . 5颞骨岩部后骨板有成角变异( 7侧) ，且以后外缘为多。
2.
Ct and mr imaging showed a densely calcified nodule with fatty bone marrow component protruding from the inner surface of petrous bone but not involving the internal auditory canal 电脑断层与磁振造影检查显示一致密钙化结节，内含脂髓，由岩骨内缘凸出，但未侵犯内耳听道。
3.
Ct and mr imaging showed a densely calcified nodule with fatty bone marrow component protruding from the inner surface of petrous bone but not involving the internal auditory canal 计算机断层与磁振造影检查显示一致密钙化结节，内含脂髓，由岩骨内缘凸出，但未侵犯内耳听道。
4.
An anterior sigmoid sinus tend to be observed when the distance between petrous back wall and external auditory canal is shorter . 5 . 11 / 40 ( 27 . 5 % ) posterior lip of internal acoustic meatus cover facial nerve more than 1 / 3 气化的乳突其颞骨岩部后骨板与外耳道后壁之间距离较大，外耳道后壁和颞骨岩部后硬脑膜之间距离也反映了乙状窦前移程度，该距离愈小，乙状窦愈有前移倾向。
