Lesson 4 Form Fundamentals: The Sphere and Organic Form
The Sphere can be described in line, without tone, by using three lines at right angles to each other wrapped around it. This arrangement is particularly useful for simplifying organic forms, especially symmetric forms such as ribcages and heads, as shall become clear below.
As for the cylinder and the rectangular prism, which by now you are hopefully fairly comfortable with, the sphere has some relatively simple rules that can solve most problems. The sphere is an extension of the first two basic forms, which is why it has been left until last.