Boa constrictor possess an elongate lung containing an anterior vascular section that abruptly changes into a saccular lung incapable of gas exchange. Measurements and analyses of data have shown that the anterior vascular portion may be compromised for ventilation during acts such as constriction and prey ingestion and that the saccular lung may actively participate in ventilation. Five snakes were instrumented with electromyograph electrodes to record the ventilatory muscle activity throughout the various regions of the lung. It was determined that the animals in this study were capable of activating the inspiratory levator costa muscle independently in the anterior and/or posterior regions and could effectively shift the site of ventilatory pumping between the vascular and saccular lungs. It was also found that locomotion precludes the levator costa from being used for ventilation, and that this muscle is co-opted for both locomotion and ventilation. These findings support the hypothesis that the saccular lung functions as a caudal bellows during times of compromised activity and indicates that the levator costa in snakes is utilized for multiple tasks.