Explanation

When light passes from a rarer to a denser medium its speed decreases, since v = c/n and the denser medium has the larger refractive index. By Snell's law (n1*sin(theta1) = n2*sin(theta2)), the ray bends toward the normal on entering the denser medium. It therefore slows down and bends toward the normal. Speeding up and bending away from the normal happens only when going from denser to rarer.