Editing Midbrain (section)

===Cerebral peduncles===
[[Image:Brain Anatomy - Mid-Fore-HindBrain.png|thumb|Brain anatomy – forebrain, midbrain, hindbrain.]]

The [[cerebral peduncle]]s each form a lobe ventrally of the tegmentum, on either side of the midline. Beyond the midbrain, between the lobes, is the [[interpeduncular fossa]], which is a cistern filled with [[cerebrospinal fluid]] {{citation needed|date=February 2017}}.

The majority of each lobe constitutes the [[cerebral crus]]. The cerebral crus are the main tracts descending from the [[thalamus]] to caudal parts of the central nervous system; the central and medial ventral portions contain the [[corticobulbar tract|corticobulbar]] and [[corticospinal tract]]s, while the remainder of each crus primarily contains tracts connecting the cortex to the [[pons]]. Older texts refer to the crus cerebri as the ''cerebral peduncle''; however, the latter term actually covers all fibres communicating with the cerebrum (usually via the diencephalon), and therefore would include much of the tegmentum as well. The remainder of the crus pedunculi – small regions around the main cortical tracts – contain tracts from the [[internal capsule]].

The portion of the lobes in connection with the tegmentum, except the most lateral portion, is dominated by a blackened band – the [[substantia nigra]] (literally ''black substance'')<ref name="Martin"/> – which is the only part of the [[primate basal ganglia|basal ganglia system]] outside the forebrain. It is ventrally wider at the rostral end. By means of the basal ganglia, the substantia nigra is involved in motor-planning, [[learning]], [[addiction]], and other functions. There are two regions within the substantia nigra – one where neurons are densely packed (the [[pars compacta]]) and one where they are not (the [[pars reticulata]]), which serve a different role from one another within the basal ganglia system. The substantia nigra has extremely high production of melanin (hence the colour), dopamine, and [[noradrenalin]]; the loss of dopamine-producing neurons in this region contributes to the progression of [[Parkinson's disease]].<ref>{{Cite journal|last1=Damier|first1=P.|last2=Hirsch|first2=E. C.|last3=Agid|first3=Y.|last4=Graybiel|first4=A. M.|date=1999-08-01|title=The substantia nigra of the human brainII. Patterns of loss of dopamine-containing neurons in Parkinson's disease|journal=Brain|volume=122|issue=8|pages=1437–1448|doi=10.1093/brain/122.8.1437|pmid=10430830|issn=0006-8950|doi-access=free}}</ref>