The elongated, limbless body of a snake is an evolutionary adaptation, raising questions about how its internal systems function. Lacking the anatomical structures of many other vertebrates, a snake’s breathing is a specialized process. The mechanics of moving air into and out of such a long, narrow body cavity have been shaped by the pressures of its form and feeding habits.
Anatomy of the Snake Respiratory System
A snake’s respiration begins at the glottis, a small opening in the floor of its mouth behind the tongue that opens directly into the trachea, or windpipe. The trachea is a long tube reinforced by C-shaped cartilaginous rings. This design provides both support and flexibility as prey passes through the esophagus, which lies just above it.
The trachea extends down the body and, in most species, leads primarily to a single functional right lung. The left lung is typically vestigial, meaning it is greatly reduced or absent. This elongated right lung extends a significant distance through the body cavity, an adaptation to their slender anatomy.
How Snakes Move Air
Unlike mammals, snakes do not have a diaphragm and instead rely on their rib cage muscles to breathe. To inhale, a snake contracts the intercostal muscles between its ribs, causing the rib cage to expand. This expansion increases the body cavity’s volume, which decreases pressure within the lung and draws air inward.
Exhalation is a more passive action, as the snake relaxes its intercostal muscles, allowing the rib cage to return to its resting position. This increases pressure on the lung, forcing air out.
Breathing During Swallowing
A snake’s ability to breathe while ingesting large prey is a process that can be extremely time-consuming. This is possible due to the mobility of the glottis. As the snake’s mouth and throat are completely filled by its meal, it can extend the glottis forward and out the side of its mouth.
This maneuver allows the tracheal opening to function like a snorkel, maintaining a clear airway while swallowing continues. The cartilage supporting the glottis and trachea provides the rigidity to be pushed forward without collapsing, which ensures that the snake can continue to take in oxygen during feeding.
Unique Lung Structures in Snakes
A snake’s functional lung is divided into two sections with different roles. The anterior portion, closer to the head, is the vascular lung, a region rich in blood vessels with a honeycomb-like structure to maximize surface area for gas exchange. Behind this is the saccular portion, which functions as an air sac.
This simpler, balloon-like part has fewer blood vessels and is not for gas exchange, but acts as a bellows to move air through the vascular lung. For some aquatic snakes, this saccular lung also aids buoyancy.