The webbing that connects the area between the human thumb and index finger is referred to as the thenar space. This area lies beneath the deep fascia, or tissues, on the palmar surface of the adductor pollicis muscle.
The first lumbrical muscle passes through the thenar space to the index finger.
In reflexology, shiatsu and acupressure disciplines, significant pressure points are located in the thenar space of the hands. The adrenal reflex point can be found here, as can the large intestine 4, a point reputed to help relieve headaches.
The word "thenar" derives from Greek and means "palm of the hand."