Inter- and Intraspecific Variations in the Pectoral Muscles of Common Chimpanzees(Pan troglodytes), Bonobos(Pan paniscus), and Humans(Homo sapiens)

We have analyzed anatomic variations in the pectoralis major and pectoralis minor muscles of common chimpanzees(Pan troglodytes)and bonobos(Pan paniscus)and compared them to anatomic variations in these muscles in humans(Homo sapiens). We have macroscopically dissected these muscles in six adultPan troglodytes, fivePan paniscusof ages ranging from fetus to adult, and five adultHomo sapiens. AlthoughPan troglodytesare thought to lack a separate pectoralis abdominis muscle, we have identified this muscle in three of thePan troglodytes; none of thePan paniscus, however, had this muscle. We have also found deep supernumerary fascicles in the pectoralis major of twoPan troglodytesand all fivePan paniscus. In all sixPan troglodytes, the pectoralis minor was inserted at the supraspinatus tendon, while, inPan paniscusandHomo sapiens, 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.