Explanation:
The diaphragm is a dome-shaped muscle located at the bottom of the thoracic cavity, separating the thoracic and abdominal cavities. It plays a crucial role in the process of respiration.

Function of the Diaphragm:
The primary function of the diaphragm is to aid in the process of breathing by increasing the volume of the thoracic cavity. When the diaphragm contracts, it moves downward, causing the volume of the thoracic cavity to increase. This creates a negative pressure within the thoracic cavity, which allows air to be drawn into the lungs. When the diaphragm relaxes, it moves upward, decreasing the volume of the thoracic cavity and causing air to be expelled from the lungs during exhalation.

Increase in Volume in the Anterior-Posterior Axis:
When the diaphragm contracts, it moves downward towards the abdominal cavity, causing an increase in the vertical dimension of the thoracic cavity. This increase in the anterior-posterior axis allows the lungs to expand vertically, facilitating inhalation. Conversely, when the diaphragm relaxes, it moves upward, decreasing the vertical dimension of the thoracic cavity and aiding in exhalation.

Increase in Volume in Other Axes:
While the diaphragm primarily increases the volume of the thoracic cavity in the anterior-posterior axis, it also has secondary effects on other axes. When the diaphragm contracts and moves downward, it also causes a slight increase in the transverse dimension of the thoracic cavity, expanding it laterally. This lateral expansion allows the lungs to expand sideways, further facilitating inhalation. However, this increase in volume in the lateral regions is not as significant as the increase in the anterior-posterior axis.

Conclusion:
In summary, the diaphragm primarily increases the volume of the thoracic cavity in the anterior-posterior axis. This increase in volume allows the lungs to expand vertically during inhalation. While the diaphragm also contributes to a slight increase in volume in the lateral regions, it is not the primary axis of expansion.