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1·When our ancestors were covered in fur, muscles in their skin called arrector pili contracted when they were upset or cold, making their fur stand on end.

当我们的祖先身体被毛发覆盖时，当人感到沮丧或者寒冷的时候皮肤上的一种叫“立肌”的肌肉会收缩，使他们的毛发竖立起来。

2·Along one side of the follicle, two buds are formed: an upper, which develops into the sebaceous gland, and a lower, which becomes the attachment for the arrector pili muscle.

毛囊的一侧形成两个胚芽：上部胚芽生长进入皮脂腺，下部胚芽形成立毛肌的附着处。