Round Ass
The round ass (often called butt, buns, bum, ass or arse) are rounded portions of the anatomy located on the posterior of the pelvic region of the great apes and humans. The buttocks are formed by the masses of the two gluteal muscles; the gluteus maximus and the gluteus medius, (aka 'the glutes'), superimposed by a layer of fat. The superior aspect of the buttock ends at the iliac crest and the lower aspect is outlined by the horizontal gluteal crease. The round ass has two insertion points: 1/3 superior portion of the linea aspera of the femur, and the superior portion of the iliotibial tractus. The masses of the gluteus maximus muscle are separated by an intermediate gluteal cleft or "crack" in which the anus is situated. They allow primates to sit upright comfortably without needing to rest their weight on their feet, as (for example) cats and dogs must do when they sit upright.
