The cord-like structure of the tendon is not the only conformation a tendon can take. The muscles of the skull are held together by tendons with the same basic building blocks (collagen), but they take a different shape. Go ahead and feel your head until you locate a dense tendon cord like the Achilles. Instead of forming a tight cord, the collagen fibers spread out into a flat, fan shape. This type of tendon is called an aponeurosis. Specifically, the top of your skull is covered by the galea aponeurotica.