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.
Gender Development. Gender refers to an individual's anatomical sex, or sexual assignment, and the cultural and social aspects of being male or female. An individual's personal sense of maleness or femaleness is his or her gender identity. Outward expression of gender identity, according to cultural and social expectations, is a gender role. Either gender may live out a gender role (a man or a woman, for instance, can be a homemaker) but not a sex role, which is anatomically limited to one gender (only a woman can gestate and give birth).