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.
Biological sex is assigned at birth, depending on the appearance of the genitals. Gender identity is the gender that a person identifies with or feels themselves to be. While biological sex and gender identity are the same for most people, this is not the case for everyone.