When it's cold, the arrector muscle pulls the hair up. The duct to the sweat glands gets small to conserve heat.
而当很冷的时候，竖毛机会使头发竖起来，汗腺的输送管也会变小来聚集热量。
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。
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。
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。
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