The Anatomy Lesson of Dr. Tulp was Rembrandt’s first major commission. The name of each of the participants is known, as well as, the prisoner, who is being dissected.
In Svetlana Alpers’ book “Rembrandt’s Enterprise: The Studio and The Market” what is really going on here is described:
It has only recently been pointed out that while the doctor’s right hand exposes the muscles and tendons, his left hand is raised in a gesture which demonstrates company speech but to demonstrate that flexing of the fingers which enables us to hold or grasp object. He is in effect demonstrating how we use our hand.”