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These three muscles are often difficult to separate from one another in the cadaver and are usually identified as the levator ani muscle.
The coccygeus muscle, attaches to the anterior surface of the sacrospinous ligament and has a fibrous appearance during the dissection.Identify the ischial spines and locate the tendinous arch of the obturator internus fascia (tendinous arch) which runs anteriorly and superiorly from the ischial spines to the lower border of the obturator canal. This arch is a thickening of the obturator internus fascia and serves as an attachment site for the iliococcygeus muscle, which is part of the levator ani muscle.
Links and References:
Grant's: 3.41
Netter (1ed.): 377, 337, 338 (2ed.): 373, 333, 334
Rohen/Yokochi: 323