Because it's an illustration, this particular image of the female body can be essentially made perfect. She's laying in a very promiscuous pose, basically like she's inviting someone to come and have sex with her. The purpose of this image is to be appealing enough that someone would want to display it. Her body is for display purposes, especially since she isn't, in fact, a real person. Since this image is vintage, her body type isn't at all like those of high fashion models today. She actually has a body that would be more likely to actually be "real."
