Facial nerve palsy at sternomastoid canal can cause-
Loss of corneal reflex at side of lesion
Loss of taste sensation anterior 2/3 of ipsilateral tongue
Loss of lacrimation at side of lesion
Hyperacusis
Below stylomastoid foramen, facial nerve gives following branches: - Posterior auricular branch, muscular branches (stylohyoid & posterior belly of digastric) and terminal (peripheral) branches.
Lesion at sternomastoid foramen : -

i)    Will spare

Greater superficial petrosal nerve → Lacrimation present.
Nerve to stapedius → Normal stapedial reflex and no hyperacusis.
Chorda tympani → Normal salivation and a taste sensation in anterior 2/3 of the tongue.

ii) Will involve

Terminal (peripheral) branches → Paralysis of muscles of facial expression. Corneal reflex will also be lost because efferent fibres of corneal reflex are derived from peripheral branches of the facial nerve.