Why is the e-ray sometimes below and sometimes above the o-ray in prisms?

[daphnelee-mh]

Homework Statement

Draw the ray and find diverged angle

Relevant Equations

Snell law (attached below)

Snell's law:

I am confused why sometimes the e-ray is below and sometimes above the o-ray? how if no>ne and how to

 

[vanhees71]

There's nothing restricting the relative magnitude of $n_{\text{o}}$ and $n_{\text{e}}$ in a uniaxial material. See, e.g., here:

https://en.wikipedia.org/wiki/Birefringence#Terminology