Dr. Nicolaes Tulp is pictured explaining the musculature of the arm to medical professionals. The corpse is that of the criminal Aris Kindt, strangled earlier that day for armed robbery. Some of the spectators are various patrons who paid commissions to be included in the painting.
The event can be dated to 16 January 1632: the Amsterdam Guild of Surgeons, of which Tulp was official City Anatomist, permitted only one public dissection a year, and the body would have to be that of an executed criminal.
Anatomy lessons were a social event in the 17th century, taking place in lecture rooms that were actual theatres, with students, colleagues and the general public being permitted to attend on payment of an entrance fee. The spectators are appropriately dressed for a solemn social occasion. It is thought that, with the exception of the figures to the rear and left, these people were added to the picture later.
One person is missing: the Preparator, whose task it was to prepare the body for the lesson. In the 17th century an important scientist such as Dr. Tulp would not be involved in menial and bloody work like dissection and such tasks would be left to others. It is for this reason that the picture shows no cutting instruments. Instead we see in the lower right corner an enormous open textbook on anatomy, possibly the 1543 De Humani Corporis Fabrica (Fabric of the Human Body) by Andreas Vesalius.
Medical specialists have commented on the accuracy of muscles and tendons painted by the 26-year-old Rembrandt. It is not known where he obtained such knowledge; it is possible that he copied the details from an anatomical textbook. However, recent Dutch research revealed several discrepancies of the exposed left forearm compared to that of a real male cadaver.
The face of the corpse is partially shaded, a suggestion of umbra mortis (shadow of death), a technique that Rembrandt was to use frequently.
The painting is signed in the top-left hand corner Rembrandt f[ecit] 1632. It is the first known instance of Rembrandt signing a painting with his forename as opposed to the initials RHL (Rembrandt Harmenszoon of Leiden), and is thus a sign of his growing artistic confidence.