The number of bicephalic ribs in human are:

Options

A. Seven pairs
B. Twelve pairs
C. Two pair
D. Three pairs

Answer

To determine the number of bicephalic ribs in humans, we need to understand what bicephalic ribs are and their characteristics.

### Step-by-Step Solution:

1. **Definition of Bicephalic Ribs**:
- Bicephalic ribs are those ribs that have two articulation surfaces on the dorsal side, meaning they connect to two vertebrae.

2. **Understanding Rib Pairs**:
- Humans have a total of 12 pairs of ribs. These ribs can be categorized into true ribs, false ribs, and floating ribs.
- True ribs (1st to 7th pairs) directly attach to the sternum.
- False ribs (8th to 10th pairs) do not attach directly to the sternum but are connected to the 7th rib.
- Floating ribs (11th and 12th pairs) do not attach to the sternum at all.

3. **Identifying Bicephalic Ribs**:
- All 12 pairs of ribs articulate with the thoracic vertebrae. However, the term "bicephalic" specifically refers to the ribs that articulate with two vertebrae.
- The first rib articulates with T1 vertebra only, but the 2nd to 10th ribs articulate with two vertebrae (the rib number and the one above it).
- Therefore, the ribs that are bicephalic are those from the 2nd to the 10th pairs.

4. **Counting Bicephalic Ribs**:
- The bicephalic ribs are the 2nd to the 10th pairs, which gives us a total of 9 pairs of bicephalic ribs.

5. **Conclusion**:
- The total number of bicephalic ribs in humans is 9 pairs.

### Final Answer:
- The number of bicephalic ribs in humans is **9 pairs**.