brachii

Brachii is a Latin term used in human anatomy as part of the official names of several upper-arm muscles. It is the genitive singular form of brachium, meaning “of the arm,” and is used to indicate that the muscle is located in or functions with the upper limb.

The best-known examples are biceps brachii and triceps brachii. Biceps brachii is the two-headed muscle on the front of the upper arm; triceps brachii is the three-headed muscle on the back of the arm. The term is not a standalone muscle name but a grammatical element, and not every arm muscle includes “brachii” in its name (for example, the brachialis).

In usage, brachii is generally treated as part of the official Latin nomenclature in medical texts. Grammatically, brachii is the genitive singular; the nominative form is brachium, and the genitive plural would be brachiorum. The adjective form meaning relating to the arm is brachial, distinct from the component in names that use brachii.