There are about 650 muscles in the body, although some authorities believe there are as many as 850 muscles. No exact figure is available because experts disagree about which are separate muscles and which ones branch off larger ones. Also, there is some variability from one person to another, though the general musculature remains the same.
The posterior muscles. (From Moore, K. L., Ph.D., FRSM, FIAC, and Dalley, A.F. II, Ph.D. Clinical Oriented Anatomy. 4th Ed. Baltimore: Lippincott, Williams & Wilkins, 1999.)