The platysma is a superficial muscle that overlaps the sternocleidomastoid. It is a broad sheet arising from the fascia covering the upper parts of the pectoralis major and deltoid; its fibers cross the clavicle, and proceed obliquely upward and medially along the side of the neck.
For example genetic differences, females inherit X chromosomes from their father giving them a genetic make-up of XX, while males inherit a Y chromosome from their father, thus giving them a genetic make-up of XY.
Three sets of factors have been proposed to explain these gender differences: biological factors (anatomy, hormones); cultural factors (the double standard, gender roles, body image); and other factors (fear of pregnancy, differences in masturbation patterns creating other gender differences).