Why do the people look like aliens in this 1895 "gynecological gymnastics" book?

The Public Domain Review came across a 19th century book called Die Heilgymnastik in der Gynaekologie.

As the title implies the gynecological exercises are based on those invented by the Swedish obstetrician and gynecologist, Thure Brandt (1819-1895). Brandt began treating women in 1861, combining massage, stretching, and general exercise as a form of treating gynecological conditions. After his methods were examined in Jena by German gynecologists in 1886, they became widely used in Europe. The images in this particular text are eye-catching today less for the gynecological technique they depict but more the bizarre similarity between the rakishly thin figures employed in demonstrating the exercises (no doubt an attempt to de-sexualise the images) and the figure of the so-called “Grey Alien” – thin body, huge head, large eyes – which wouldn’t hit popular consciousness for another 65 years.