This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
Which of the following is the largest and most impoant muscle in the pelvic floor? 
Select and explain. 
A. Coccygeus, B. External anal sphincter, C. Levator ani, D. Obturator internus
C: Levator ani
Answer: C: Levator ani 
Explanation: The pelvic floor is formed by the large levator ani (with pas including the pubococcygeus, puborectalis, and iliococcygeus) and the much smaller coccygeus. The small external anal sphincter lies below the levator ani and is not technically pa of the pelvic floor. The obturator internus is in the lateral wall of the pelvis. Ref: Hoffman B.L., Schorge J.O., Schaffer J.I., Halvorson L.M., Bradshaw K.D., Cunningham F.G., Calver L.E. (2012). Chapter 38. Anatomy. In B.L. Hoffman, J.O. Schorge, J.I. Schaffer, L.M. Halvorson, K.D. Bradshaw, F.G. Cunningham, L.E. Calver (Eds), Williams Gynecology, 2e.