Which lung is the larger, functional lung in most snakes?

In most snakes, the right lung is the larger and functional lung.

Snake bodies are long and narrow, so their internal organs have evolved unusual arrangements. The right lung extends much farther along the body and performs most of the breathing work. In many species, the left lung is greatly reduced or absent, leaving room for other organs in the confined body cavity.

A reduced left lung is not universal. Some primitive snakes retain a more substantial left lung, while the right lung remains dominant across snakes generally. The rear portion of the right lung can also be modified into an air sac, helping maintain airflow and possibly supporting buoyancy in aquatic species.

This respiratory asymmetry is one of several adaptations associated with the snake’s elongated form. Snakes also lack a diaphragm, so movements of the ribs and body wall help ventilate the lungs. The arrangement is efficient despite looking very different from mammalian anatomy.