Demifacets present at `:-`

Options

A. Thoracic vertebra
B. Lumbar vertebra
C. Sacral vertebra
D. Cervical vertebra except `C_(7)`

Answer

### Step-by-Step Solution:

1. **Understanding Demifacets**:
- A demifacet is defined as half of a facet, which is a flat or nearly flat surface on a bone. In the context of vertebrae, demifacets are associated with the articulation of ribs.

2. **Identifying Vertebrae Types**:
- There are four types of vertebrae mentioned: thoracic, lumbar, sacral, and cervical (excluding C7).

3. **Thoracic Vertebrae**:
- There are 12 thoracic vertebrae (T1 to T12). Each of these vertebrae has facets on their bodies and transverse processes that articulate with the ribs.

4. **Role of Demifacets**:
- The head of a rib articulates with two thoracic vertebrae through the costal demifacets. This means that the demifacets are specifically present on the thoracic vertebrae to facilitate this connection.

5. **Other Vertebrae**:
- **Lumbar Vertebrae**: There are 5 lumbar vertebrae, which do not have demifacets as they do not articulate with ribs.
- **Sacral Vertebrae**: The sacral vertebrae form a triangular bone and are fused, also lacking demifacets.
- **Cervical Vertebrae**: The cervical vertebrae (except C7) have transverse foramina but do not have demifacets.

6. **Conclusion**:
- Based on the information discussed, demifacets are present only in the thoracic vertebrae.

### Final Answer:
- **Demifacets are present at thoracic vertebrae.**