what is the muscle between your thumb and pointer finger

Those from C8 and T1 form the superior trunk. Those from C5 and C6 join to form the superior trunk. The anterior branches from C5-T1 are termed roots of the brachial plexus. The mixed spinal nerves give off posterior and anterior branches. The mixed spinal nerves join to form the brachial plexus (Latin brachium = arm). The entirety of the spinal cord gives off eight cervical, twelve thoracic, five lumbar, five sacral, and one coccygeal mixed spinal nerve. Those that serve the upper limb are derived from spinal cord segments C5-T1. The posterior and anterior roots join to form the mixed spinal nerve. The anterior roots are motor in function. The cell bodies for motor function lie in the anterior (ventral) gray horns. They have a peripheral process that innervates the organs of sensation in the skin and a central process that connects the posterior root ganglia to the spinal cord posterior (dorsal) columns for sensory function. The sensory neurons have their cell bodies in the posterior (dorsal) root ganglia.

The spinal cord is divided into white columns (myelinated axons) and gray horns (cell bodies of motor neurons). These muscles are innervated by C5-T1 spinal nerves.

The innervation of the upper limb is divided into anterior (ventral) divisions that supply the anterior muscles (such as biceps brachii, brachialis, pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis and profundus, and pronator quadratus).

What is the muscle between your thumb and pointer finger