Which of the following ribs are not connected ventrally with the stenum and are called as floating ribs ?

Options

A. First five pairs
B. `8 ^(th) , 9^(th) and 10^(th)`pairs
C. `11^(th ) and12^(th)`pair
D. `7^(th), 8^(th) and 9^(th) ` pairs

Answer

To answer the question regarding which ribs are not connected ventrally with the sternum and are referred to as floating ribs, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of Ribs**: Ribs are classified into three main categories based on their connection to the sternum: true ribs, false ribs, and floating ribs.

2. **Identify True Ribs**: True ribs are the first seven pairs of ribs (1st to 7th). They are attached dorsally to the thoracic vertebrae and ventrally to the sternum via hyaline cartilage.

3. **Identify False Ribs**: False ribs consist of the 8th, 9th, and 10th pairs. These ribs are connected to one another and indirectly to the sternum, but not directly attached to it.

4. **Identify Floating Ribs**: Floating ribs are the 11th and 12th pairs. These ribs are only attached dorsally to the thoracic vertebrae and do not connect ventrally to the sternum, which is why they are termed "floating."

5. **Evaluate the Options**:
- The first option lists the first five pairs of ribs, which are true ribs. This option is incorrect.
- The second option lists the 8th, 9th, and 10th pairs, which are false ribs. This option is also incorrect.
- The third option lists the 11th and 12th pairs, which are indeed the floating ribs. This option is correct.
- The last option lists the 7th, 8th, and 9th pairs, where the 7th is a true rib and the 8th and 9th are false ribs. This option is incorrect.

6. **Conclusion**: The correct answer to the question is that the ribs which are not connected ventrally with the sternum and are called floating ribs are the **11th and 12th pairs**.