pinnas

Pinnas is the plural form of pinna, and the term is used in biology to refer to more than one of these structures in different contexts. The most common senses are anatomical and botanical.

In anatomy, the pinna, or auricle, is the visible external part of the ear. It serves to collect sound waves and funnel them into the ear canal, while its distinctive shape helps with the localization of sounds in the vertical plane. The pinna is composed mainly of a flexible cartilage frame covered by skin, with recognizable landmarks such as the helix, antihelix, tragus, antitragus, concha, and lobule. Sensory innervation of the pinna comes from branches of the facial and lesser occipital nerves, among others, and its blood supply is provided by arteries including the posterior auricular and superficial temporal arteries. The pinna can be affected by conditions ranging from congenital malformations to trauma, and its structure often bears variation among individuals.

In botany, a pinna is a primary division of a compound leaf, particularly on ferns. A frond may bear pinnae along a central rachis, and each pinna can be further divided into smaller leaflets called pinnules. Leaves with pinnae can be arranged in pinnate, bipinnate, or tripinnate patterns, affecting the overall shape and photosynthetic surface area of the plant. The term helps describe the morphology of many fern species as well as some flowering plants with compound leaves.

Etymology traces pinna to Latin, meaning feather or wing. In English usage, pinnas is often found as the plural in anatomical references, while pinnae remains standard in botanical contexts.