What anatomical structure encapsulates the outer ear?

The outer ear, also known as the pinna or auricle, is primarily composed of a skin-covered, flexible cartilaginous structure. This unique anatomical configuration allows the outer ear to maintain its shape while also being lightweight and capable of directing sound waves into the ear canal. The cartilage provides both flexibility and durability, allowing the pinna to withstand minor impacts without sustaining damage.

In addition to facilitating sound collection, the skin covering the cartilage also plays a crucial role in protecting the ear from environmental factors such as dirt and moisture. This combination of structural support and protective covering is essential for the outer ear's function in hearing and protecting the more delicate structures found deeper within the ear.

Other options represent structures that do not accurately describe the outer ear. The bony structure refers more typically to the middle and inner ear components, while a fibrous membrane is more related to other anatomical features, such as various body cavities or areas (e.g., tympanic membrane). A fluid-filled sac generally describes other physiological structures, such as the inner ear's semicircular canals or vestibular system, and is not relevant to the outer ear's composition.