............ and ............ pairs of ribs are called floating ribs.

Explanation

To answer the question about which pairs of ribs are called floating ribs, we can follow these steps:

1. **Identify the Context**: Understand that the question is asking for specific pairs of ribs that are classified as floating ribs.

2. **Recall the Anatomy of Ribs**: In human anatomy, ribs are categorized into three types: true ribs, false ribs, and floating ribs. True ribs are directly attached to the sternum, false ribs are indirectly attached, and floating ribs are not attached to the sternum at all.

3. **Determine the Specific Pairs**: The floating ribs are specifically the last two pairs of ribs in the rib cage. These are the 11th and 12th pairs.

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