**Core Concept**
The deltoid ligament, also known as the medial ligament of the ankle, is a strong, fan-shaped ligament that provides medial stability to the ankle joint. It is composed of four distinct bands: the tibiocalcaneal, tibiotalar, tibiobiblical, and anterior tibiotalar ligaments.

**Why the Correct Answer is Right**
The deltoid ligament is attached to the medial malleolus, talus, and calcaneum via the tibiocalcaneal, tibiotalar, and tibiobiblical ligaments, respectively. These attachments provide medial support and stability to the ankle joint. The deltoid ligament is a crucial structure in maintaining the medial aspect of the ankle, and its attachments are well-defined and understood in anatomy.

**Why Each Wrong Option is Incorrect**
* **Option A:** The medial malleolus is indeed one of the attachments of the deltoid ligament, making this option incorrect.
* **Option B:** The talus is also attached to the deltoid ligament via the tibiotalar ligament, which makes this option incorrect.
* **Option C:** The calcaneum is attached to the deltoid ligament via the tibiocalcaneal ligament, making this option incorrect as well.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the deltoid ligament is a strong, fan-shaped ligament that provides medial stability to the ankle joint. Its attachments are well-defined, and understanding these is crucial for diagnosing and managing ankle injuries.

**Correct Answer:**
✓ Correct Answer: D. Lateral malleolus. The deltoid ligament is not attached to the lateral malleolus, which is instead supported by the anterior and posterior inferior tibiofibular ligaments.