气管细胞的主要结构为一层多扁平细胞组成，称管壁细胞层，细胞层分泌的表皮几丁质形成气管内壁，内壁加厚成螺旋盘绕状的内脊，称为螺旋丝。螺旋丝有弹力并有抵抗压力的能力，以保持气管成圆筒形而利于气体的交换。
当垂直刀架下降时，由于摩擦力阻碍其下降，使丝杆的上螺旋面螺母的下螺旋面相接触，丝杆螺母的间隙在下面。
When the vertical turret decline, due to friction hinder its decline, the screw on helical screw nut under the physiognomy contact screw nut in the space below.
螺旋装：把书页在装订边打孔，用连续的金属丝作螺纹式穿过的装订方法。参阅机械式装订。
Spiral binding: a method of binding in which a continuous wire is threaded through holes punched in the binding edge of the pages. see mechanical binding.
均采用直丝弓矫治器矫治，应用螺旋推簧扩展间隙及上颌前方牵引。
They were all treated with straight wire appliance and helical spring to expand clearance.
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