Which of the following regions is directly above the costal margin?

The region that is directly above the costal margin is indeed the umbilicus. The costal margin is formed by the lower edges of the rib cage, and it serves as a point of reference for anatomical locations. The umbilicus, or belly button, is situated near the center of the abdomen, just below the rib cage. This alignment means that the umbilicus is anatomically positioned directly above the costal margin.

In contrast, the other regions mentioned do not have the same anatomical relationship to the costal margin. The pectoral girdle is located at the upper part of the body and includes the clavicles and scapulae but does not lie directly above the costal margin. The submental region is situated beneath the chin, which is well above the costal margin. The temporal region refers to the sides of the head, located above the jaw and well above the costal margin as well.

Therefore, the umbilicus is specifically located in the abdominal area, directly in line with the costal margin, making it the appropriate choice.