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 identity is one's personal experience of one's own gender. Gender identity can correlate with assigned sex at birth, or can differ from it completely. All societies have a set of gender categories that can serve as the basis of the formation of a person's social identity in relation to other members of society.