**Core Concept**
The deltoid ligament, also known as the medial ligament of the ankle joint, is a complex structure that provides medial stability to the ankle. It is composed of two layers: superficial and deep. The superficial layer consists of four ligaments: the tibiocalcaneal, tibiotalar, tibionavicular, and the interosseous ligament. The deep layer consists of two ligaments: the tibiocalcaneal and the tibiotalar.

**Why the Correct Answer is Right**
The deltoid ligament is a critical ligamentous structure that provides medial stability to the ankle joint. It is attached to the medial malleolus of the tibia, which is a bony prominence on the inner aspect of the ankle. The deltoid ligament is attached to several bones, including the talus, calcaneum, and navicular bone. However, it is not attached to the lateral malleolus, which is a bony prominence on the outer aspect of the ankle. The lateral malleolus is instead connected to the anterior talofibular ligament, which is a separate ligamentous structure.

**Why Each Wrong Option is Incorrect**
**Option A:** The deltoid ligament is indeed attached to the medial malleolus, which serves as its origin. Therefore, this option is incorrect.
**Option B:** The deltoid ligament is attached to the talus, which is a crucial bone that articulates with the tibia and calcaneum in the ankle joint. This option is therefore incorrect.
**Option C:** The deltoid ligament is also attached to the calcaneum, which is a flat bone that forms the heel of the foot. This option is incorrect as well.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the deltoid ligament is a complex structure with multiple attachments, and its injuries can lead to medial ankle instability. A thorough understanding of the deltoid ligament's anatomy is crucial for diagnosing and managing ankle injuries.

**✓ Correct Answer: D. Lateral malleolus** The deltoid ligament is not attached to the lateral malleolus.