Bilateral Chondroepitrochlearis Muscle: Case Report, Phylogenetic Analysis, and Clinical Significance

Figure 4

Collage of schematic drawings of the left thorax and upper limb of three different species. Black arrows depicting the direction of force of the pectoralis major muscle. At the end of a forelimb cycle of the dog (terrestrial quadruped), the forelimb needs to be drawn forward; hence the direction of PM is anterior. For the gorilla (arboreal bipedal), the forelimb can be further dragged down towards the midaxillary line due to the fiber direction of PM. In the human (terrestrial bipedal), one can draw the human’s upper limb up to the midaxillary line well beyond the range of dog due to the change of insertion of the PM.

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