**Core Concept**
Posterior epistaxis refers to bleeding from the posterior nasal cavity, which is often due to the rupture of the posterior ethmoidal artery or the sphenopalatine artery. To control severe bleeding, surgical intervention may be required, including ligation of the relevant artery.

**Why the Correct Answer is Right**
The sphenopalatine artery is the primary source of posterior epistaxis, accounting for approximately 90% of cases. Ligation of this artery is a common surgical procedure to control severe bleeding. The procedure involves clipping or ligating the artery at its origin in the pterygopalatine fossa, thereby reducing blood flow to the posterior nasal cavity.

**Why Each Wrong Option is Incorrect**
**Option A:** The posterior ethmoidal artery can be a source of posterior epistaxis, but it is not the primary artery involved, making ligation less frequently necessary.
**Option B:** The anterior ethmoidal artery primarily supplies the anterior nasal cavity, making it an unlikely source of posterior epistaxis.
**Option C:** The internal maxillary artery is a major branch of the external carotid artery, but it is not directly involved in posterior epistaxis.

**Clinical Pearl / High-Yield Fact**
In cases of posterior epistaxis, it is essential to identify the source of bleeding accurately before proceeding with surgical intervention, as ligation of the wrong artery can lead to further complications.

**Correct Answer:** . Sphenopalatine