Figure 6.

Pectoralis major muscle. (A) Frontal view of the reconstructed pectoralis major portions of a stage 23 human embryo (56–60 days of development), specimen number 950. All other muscles are hidden. Depicted are three heads of the pectoralis major: clavicular head (light blue), sternocostal head (red) and abdominal head (yellow) and bones (white). (B) Transverse section of the left shoulder region. The pectoralis major muscle is divided into three heads at this stage and is therefore even more partitioned than in adults (Gilroy et al. 2009). The tree heads of the left pectoralis muscle and the second rib and humerus of the same specimen as in (A) are tagged. AH, abdominal head; CH, clavicular head; PM, pectoralis major muscle; SCH, sternocostal head. Scale bar: ~5 mm.