Final answer:
A large, deep-chested thorax requires lateral rotation for breathing, facilitated by the muscles of the chest and the anatomical structure of thoracic vertebrae.
Step-by-step explanation:
A large, deep-chested thorax requires lateral rotation. The muscles involved with thorax movements include the pectoralis major and minor, as well as the intercostal muscles and the diaphragm. During inhalation, the chest expands due to the flattening of the diaphragm and the outward movement of the ribs facilitated by these chest muscles, enabling lateral rotation.
The thoracic vertebrae have a configuration that allows certain types of movement, such as rotation. A deep-chested thorax has a larger thoracic cavity, requiring a greater range of motion for the expansion and contraction essential for breathing. Consequently, because the thoracic vertebrae allow lateral rotation, a deep-chested thorax would align with this permitted movement.
The superior articular processes of the thoracic vertebrae, which face anteriorly, and the inferior processes, which face posteriorly, determine the range of movements. This anatomical structure supports the necessity for lateral rotation in a deep-chested thorax.