Complex sentence: The most well-known and important efferent projection of the substantia nigra is the nigrostriatal projection, which originates chiefly in the pars compacta, but also includes a smaller number of other dopaminergic cells scattered throughout the pars reticulata.
Split into simpler sentences: The most well-known and important efferent projection of the substantia nigra is the nigrostriatal projection. This originates chiefly in the pars compacta, but also includes a smaller number of other dopaminergic cells scattered throughout the pars reticulata.