Perspective doesn’t apply just to architecture. Everything
follows its laws, including people and animals. Some perspective
teachers suggest drawing a box around an animal, and that’s a
good idea. An even simpler idea is to draw a set of lines across
the form of any animal or person. It’s a quick way check the
placement of all the features. If they’re out of position,
you’ll know right away. In these zoo sketches of a hippo, each
head has a set of parallel lines to make sure the ears, eyes,
and nostrils are kept in their proper relationship. In the top
sketch, I’ve also lightly drawn the center line of the form. I
tried to simplify the lighting by massing the shadow as a light,
uniform tone. In the lower sketch, I simplified the forms a bit
(note the spherical forms around the eyes). The shading lines
follow the cross-section contours, which helps even more to
describe the form.