By the contraction in which of the following muscle, does the volume of the thoracic chamber increase in the anteroposterior axis?

Diaphragm muscles.

The correct answer is Option (1) - Diaphragm muscles.

Inspiration is initiated by the contraction of the diaphragm which increases the volume of the thoracic chamber in the anteroposterior axis.

The contraction of external intercostal muscles lifts up the ribs and the sternum causing an increase in the volume of the thoracic chamber in the dorso-ventral axis.

The overall increase in the thoracic volume causes a similar increase in pulmonary volume.

An increase in pulmonary volume decreases the intra-pulmonary pressure to less than the atmospheric pressure which forces the air from outside to move into the lungs, i.e., inspiration.