**Core Concept**
The greater cornua of the hyoid bone are two long, pointed processes that project anteriorly from the upper surface of the body of the hyoid bone. They play a crucial role in the movement of the hyoid bone during swallowing and speech.

**Why the Correct Answer is Right**
The greater cornua are connected to the body of the hyoid bone by cartilaginous joints, allowing for a wide range of motion. The hyoid bone is a vital structure in the neck, serving as an attachment point for several muscles, including the digastric, stylohyoid, and geniohyoid muscles. The mobility of the greater cornua is essential for the proper functioning of these muscles during various activities like swallowing and speech.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as the greater cornua are not connected to the body of the hyoid bone by synovial joints, which are characterized by a joint space and a synovial fluid-filled cavity.
* **Option B:** This option is incorrect as the greater cornua do not unite with the body of the hyoid bone at the superior cornu.
* **Option C:** This option is incorrect as the greater cornua do not unite with the body of the hyoid bone at the inferior cornu.

**Clinical Pearl / High-Yield Fact**
The hyoid bone is a vital landmark in head and neck surgery, and its mobility is essential for the proper functioning of surrounding muscles. The greater cornua of the hyoid bone are often involved in injuries to the neck, particularly in cases of strangulation or blunt trauma.

**Correct Answer: D.**