Inter- and Intraspecific Variations in the Pectoral Muscles of Common Chimpanzees , Bonobos , and Humans .

We have analyzed anatomic variations in the pectoralis major and pectoralis minor muscles of common chimpanzees and bonobos and compared them to anatomic variations in these muscles in humans . We have macroscopically dissected these muscles in six adult , five of ages ranging from fetus to adult, and five adult . Although are thought to lack a separate pectoralis abdominis muscle, we have identified this muscle in three of the ; none of the , however, had this muscle. We have also found deep supernumerary fascicles in the pectoralis major of two and all five . In all six , the pectoralis minor was inserted at the supraspinatus tendon, while, in and , it was inserted at the coracoid process of the scapula. Some of the anatomic features and variations of these muscles in common chimpanzees and bonobos are similar to those found in humans, therefore enhancing our knowledge of primate comparative anatomy and evolution and also shedding light on several clinical issues.