An academic drawing of Apollo by Joseph Emmanuël Gauguin. The drawing is likely based on the Apollino cour Carree in the Louvre.
Here's a modern reproduction Hans Effenberger.
The French copies may be based on Giorgio Sommer's sculpture of Apollo in Florence, the Apollino or Medici Apollo (left).
A bronze copy from the 18th century in the Walters Art Museum (right).
The drawing shown here is for sale on Ebay.
There are similar sculptures such as the Lycian Apollo in the Louvre.
Above is an engraving of the sculpture from The George Glazer Gallery, and another view of the sculpture in the Louvre.
The type of Apollo Statue is based on a first century BCE of a sculpted figure with the hand resting on the head. Wikipedia entry about the Lycean Apollo
Another version attributed to Francesco Righetti
The Art Student's Guide to the Bones and Muscles of the Human Bodyand Lessons on Foreshortening
The Louvre Sculpture
La Sculpture française (French Edition)