Russell Meyers has defined the extrapyramidal system as that part of the motor system that is not pyramidal. And if that doesn't help, look at the area anatomically and call it the basal ganglia. But how many nuclei should be included is also not clear; nor are the 35 contributors to the 33 chapters clear on it either. But we can accept a fluidity of boundaries these days in every aspect of life, so it really doesn't matter.
This elegant book, which no neurologic library can afford to be without (and which no neurologist can afford), is an excellent gathering of information on clinical aspects of various diseases of the structures, including Parkinson's disease, Wilson's disease, Huntington's and other choreas, and various dystonic diseases. The contributors are eminent in their fields, including such familiar names as Mettler, Raymond Adams, Denny-Brown, Schwab, and Purdon Martin. Function is covered generally and not