Final answer:
The shape of the angulus oris sulcus in youth varies and is influenced by the underlying orbicularis oris muscle and the elasticity of the skin. It does not conform to a single shape such as round, oblong, triangular, or square.
Step-by-step explanation:
In youth, the shape of the angulus oris sulcus, which is the groove at the corners of the mouth, does vary in shape. This area is influenced by the structures beneath the skin, including the orbicularis oris muscle responsible for the movement of the mouth. The angulus oris sulcus is not strictly round, oblong, triangular, or square but can be better described as a flexible contour that changes with facial movements.
The lips and the underlying musculature, such as the orbicularis oris, facilitate various functions, including speech and eating. This musculature plays a role in forming the angulus oris sulcus as it contracts and relaxes. Youthful skin also contributes to the less defined shape of the sulcus due to its elasticity and collagen content.