Ventral tegmental decussation in cerebral peduncle is due to -

Ans. is 'd' i.e., Rubrospinal tract o Midbrain is divided into following parts1) Tectum:# It is the part posterior to cerebral aqueduct. It is made up of two collicoli on each side (right and left): Superior colliculus and inferior colliculus.2) Cerebral peduncle:# It is the part anterior to cerebral aqueduct. Each cerebral peduncle is subdivided into (a) Crus cerebri (anteriorly), (b) Substantia nigra (in middle), and (c) Tegmentum (posteriorly).o Cerebral puduncle has following pathways -A. At the level of inferior colliculusi) Crus cerebri contains : (a) Middle two-third is occupied by corticospinal, and corticobulbar (corticonuclearfibres) ; (b) Medial one-sixth is traversed by frontopontine fibres; and (c) Lateral one-sixth contains temporopontine, parietopontine and occipitopontine fibres.ii) Tegmentum contains : (a) Lemnisci: (medial, trigeminal, spinal and lateral); (b) Decussation of superior cerebellar peduncles; (c) Tectospinal and rubrospinal tract, and (d) Medial longitudinal bundle.B. At the level of superior colliculusi) Crus cerebri has same tracts as described above.ii) Tegmentum has : (a) Lemnisci; (b) Dorsal tegmental decussation (formed by decussation of tectospinal and tectobulbar tracts); (c) Ventral tegmental decussation (formed by decussation of rubrospinal tract);(d) Medial longitudinal bundle, and (e) Emerging fibers of occulomotor nerve.iii) Tectum shows posterior commisure connecting two superior colliculi.