`11^(th)` and `12^(th)` pair of ribs which are imperfectly formed and do not reach the sternum are called

Options

A. Pseudo
B. fa,se ribs
C. floting ribs
D. visceral ribs.

Explanation

To answer the question regarding the 11th and 12th pair of ribs, which are imperfectly formed and do not reach the sternum, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Rib Structure**:
- The human rib cage consists of 12 pairs of ribs. Each rib is a thin, flat bone that articulates with the vertebral column at the back and, in most cases, with the sternum (breastbone) at the front.

2. **Classification of Ribs**:
- Ribs are classified into three categories:
- **True Ribs**: The first 7 pairs (1st to 7th) are called true ribs because they connect directly to the sternum.
- **False Ribs**: The 8th, 9th, and 10th pairs are known as false ribs because they do not attach directly to the sternum; instead, they connect to the 7th rib.
- **Floating Ribs**: The 11th and 12th pairs are termed floating ribs. They are not connected to the sternum or to the other ribs in the front.

3. **Identifying the Correct Term**:
- Since the question specifically asks about the 11th and 12th pairs of ribs, we can conclude that they are called **floating ribs** because they do not reach the sternum and are only attached at the back to the vertebral column.

4. **Final Answer**:
- Therefore, the answer to the question is that the 11th and 12th pairs of ribs are called **floating ribs**.