**Core Concept**
The epicranial aponeurosis (galea aponeurotica) is a tough fibrous layer that lies deep to the scalp, providing attachment for the frontalis and occipitalis muscles. The scalp is composed of multiple layers, each with distinct characteristics.

**Why the Correct Answer is Right**
The correct answer is A. A layer containing blood vessels. The scalp is divided into five layers: the skin, subcutaneous tissue, a layer of loose connective tissue, the galea aponeurotica, and the periosteum. The layer overlying the epicranial aponeurosis is the subcutaneous tissue, which contains blood vessels, nerves, and loose connective tissue. This layer provides a rich vascular supply to the scalp and is responsible for the profuse bleeding observed in the patient's wound.

**Why Each Wrong Option is Incorrect**
**Option B:** The dura mater is the outermost meningeal layer that covers the brain and spinal cord, not the structure overlying the epicranial aponeurosis.
**Option C:** The periosteum (pericranium) is a layer of connective tissue that covers the inner surface of the skull bones, deep to the galea aponeurotica. It is not the layer overlying the epicranial aponeurosis.
**Option D:** The tendon of the epicranial muscles (occipitofrontalis) is attached to the epicranial aponeurosis, but it is not the layer overlying this structure.

**Clinical Pearl / High-Yield Fact**
The scalp has a rich blood supply, with a high concentration of blood vessels in the subcutaneous tissue. This is why scalp wounds often bleed profusely, as seen in the patient's case.

**✓ Correct Answer: A. A layer containing blood vessels.**