The suprascapular ligament seems to serve no defined function in the human. A comparative study was undertaken to elucidate its function. The suprascapular region was dissected in species representing seven existing primate families and six subprimate families. A striking dichotomy of pattern was observed. In the New World primates, the suprascapular ligament appeared to be continuous with the coracoclavicular ligament; the former merely served to increase the area of bony attachment of the coracoclavicular ligament. In the Old World monkeys and subprimate mammals, the suprascapular ligament was entirely absent. The human anatomy was comparable to that found in the New World primates. This dichotomy of pattern seems to be related to the function of the upper extremity in the different classes of mammals.