In tonsillar herniation, parts of the cerebellum, called cerebellar tonsils, slip down through an opening in the skull called the foramen magnum.

在扁桃体疝中，小脑的一部分，即小脑扁桃体，经过枕骨大孔被挤压推出颅骨。

Now a myelomeningocele is typically associated with a condition called an Arnold Chiari II malformation, which is where cerebellar and brainstem tissue slip down into the foramen magnum, the opening at the base of the skull.

脊髓脊膜膨出通常与小脑扁桃体下疝（Arnold–Chiari）畸形Ⅱ型有关，即小脑和脑干组织从颅腔底部的枕骨大孔疝出。

In upward herniation, there's a displacement of the cerebellum upward, through a notch in the tentorium cerebelli, while in tonsillar herniation, parts of the cerebellum slip down through an opening in the skull called the foramen magnum.

小脑幕切迹上疝指的是小脑经过小脑幕切迹被向上挤压；小脑扁桃体下疝指的则是小脑部分组织经过枕骨大孔向下疝出。