Final answer:
The muscle that inserts onto the Pisiform, hook of the hamate, and base of the 5th metacarpal is called the Flexor retinaculum.
Step-by-step explanation:
The muscle that inserts onto the Pisiform, hook of the hamate, and base of the 5th metacarpal is called the Flexor retinaculum. The flexor retinaculum is a strong ligament that extends over the palmar surface of the hand and is attached to the trapezium, scaphoid, hamate, and pisiform bones. This ligament forms the roof of the carpal tunnel, through which the tendons of nine muscles of the anterior forearm and a nerve pass to enter the hand.