The small, backward-facing fold of skin on a cat’s outer ear is a feature that prompts curiosity in many owners. This structure is a highly developed part of the feline auditory apparatus. While this fold exists in other mammals, its prominence in the domestic cat suggests a functional advantage for a specialized predator, enhancing the cat’s remarkable senses and communication methods.
Identifying the Cutaneous Marginal Pouch
The proper anatomical name for this ear flap is the cutaneous marginal pouch, commonly known by the informal moniker, Henry’s Pocket. This fold is consistently located on the lower, posterior edge of the pinna, which is the external, visible part of the ear. The pouch presents as a small slit or pocket of skin that is part of the overall structure of the ear. It is a universal feature present in all breeds of domestic cats.
The Acoustic Role in Sound Localization
The primary hypothesis for the existence of this fold centers on its role in amplifying or filtering sound, which helps the cat pinpoint the source of noises. Cats possess one of the broadest hearing ranges among mammals, capable of detecting sounds up to 85 kilohertz (kHz). This wide range is particularly sensitive to the high-pitched sounds made by small prey, such as the ultrasonic vocalizations of mice, which fall between 22 and 70 kHz.
It is theorized that the cutaneous marginal pouch assists in the precise localization of these high-frequency sounds. The pocket may act by creating subtle reflections or echoes of incoming sound waves. This differential processing allows the cat’s brain to calculate the exact direction and distance of the noise source with greater accuracy.
The fold may also help filter out lower-frequency background noise that might interfere with hearing prey. By potentially attenuating or delaying the lower pitches, the pouch could allow the higher-frequency sounds to be perceived more clearly. This enhancement provides an evolutionary advantage to a solitary hunter that relies on detecting minute sounds.
Facilitating Ear Movement and Nonverbal Communication
Beyond acoustics, the ear flap contributes to the incredible mobility of the feline pinna, which is powered by an average of 32 individual muscles. This musculature allows a cat to rotate each ear independently by up to 180 degrees to scan the environment for sounds without moving its head. The flexible fold of the cutaneous marginal pouch may provide the necessary slack and pliability to allow the pinna this extensive range of motion.
The fold ensures that the skin and cartilage do not become taut or restrictive during extreme ear movements. This flexibility is also important for nonverbal communication, which is a major function of the cat’s ears. When a cat flattens its ears tightly against its head—a common signal of fear, aggression, or defense—the cutaneous marginal pouch acts as a fold point.
This action allows the ears to collapse fully and efficiently. This serves two purposes: protecting the delicate inner ear from a physical threat and visually communicating a state of distress or hostility to other animals. The small pocket is a structural component that supports both the cat’s specialized directional hearing and its complex body language.