Scalp Anatomy: Why Humans Have Only One Scalp

The scalp is the specialized soft tissue envelope covering the calvaria (skull vault). It consists of five layers (SCALP mnemonic):

1. Skin — thick, hair-bearing, sebaceous.
2. Connective tissue (superficial fascia) — dense, vascular, nerves.
3. Aponeurosis (galea aponeurotica) — tough tendon sheet connecting frontalis and occipitalis.
4. Loose areolar tissue — "danger zone"; allows scalp mobility, spreads infection.
5. Pericranium (periosteum) — adherent to calvarial bones.

Anatomically, the scalp is a single continuous structure from supraorbital ridges to external occipital protuberance and temporal lines. There is no duplication or segmentation into multiple scalps. Congenital anomalies (cutis aplasia, encephalocele) involve defects, not duplication.