Metathalamus

It is composed of medial and lateral geniculate bodies. All these, on the inferior aspect of the posterior part of the thalamus, lateral to every side of the midbrain are small rounded altitudes. The medial and lateral geniculate bodies are relay stations for the auditory and visual pathways, respectively.

Medial Geniculate Body

Lateral to the superior colliculus, the medial geniculate body is an oval elevation on the inferior aspect of the pulvinar of the thalamus. In relation to the lateral geniculate body. It is more notable. The inferior brachium runs upward, laterally and forwards from inferior colliculus of the midbrain to the medial geniculate body.

The inferior brachium carries auditory nerve impulses to the lateral geniculate body for onward transmission to the (primary auditory area of the) cerebral cortex.

Lateral Geniculate Body

Lateral geniculate body is a small ovoid bulge observable in the terminal end of the optic tract. It’s situated on the inferior surface of the pulvinar, anterolateral to the medial geniculate body. It’s smaller compared to the medial geniculate body and linked to the superior colliculus by the superior brachium.

The fibres of superior brachium are concerned with the creation of visual reflexes like turning of head and eyes toward the unexpected flash of light and constriction of pupil when light falls or is thrown on the retina.

The lateral geniculate body gets retinal fibres of both the eyes (from temporal half of the retina of precisely the same side and nasal half of the retina of the opposite side) via optic tract and supplies rise to fibres of the optic radiation which express visual nerve impulses to the visual cortex of the occipital lobe.