Question

the ______ are the four masses on the posterior of the midbrain.
reticular formation
choroid plexuses
corpora quadrigemina
cerebral peduncles
substantia nigra

Explanation:

• Reticular formation: A network of nerve fibers and cells throughout the brainstem, not four masses on the midbrain's posterior.
• Choroid plexuses: Structures in ventricles that produce cerebro - spinal fluid, not related to midbrain masses.
• Corpora quadrigemina: Composed of two superior colliculi (visual reflexes) and two inferior colliculi (auditory reflexes), located on the posterior of the midbrain.
• Cerebral peduncles: Part of the midbrain's anterior, involved in motor pathways.
• Substantia nigra: A midbrain structure involved in motor control (dopamine - producing), not four masses on the posterior.

Answer:

corpora quadrigemina