Washington Master Esthetics Practice Exam

Which muscle may not be present in all individuals?

1. Gastrocnemius

2. Tertius peroneus

3. Rectus femoris

4. Deltoid

The correct answer is: Tertius peroneus

The tertius peroneus is a muscle that is not universally present in all individuals. It is an anatomical variation that may emerge in some people as an accessory muscle in the lower leg, specifically assisting in ankle dorsiflexion and eversion. Its absence in others exemplifies the natural variability of human anatomy. In contrast, the gastrocnemius, rectus femoris, and deltoid muscles are considered to be fundamental components of human musculature, typical of the majority of people. The gastrocnemius is a key muscle in the calf, contributing to movements such as walking and running. The rectus femoris is one of the quadriceps muscles, playing a crucial role in knee extension and hip flexion. The deltoid is the primary muscle responsible for shoulder abduction, necessary for raising the arm. These muscles are generally present in all individuals, which contrasts with the occasional presence of the tertius peroneus.