The belly button, or umbilicus, is a feature found on nearly every human, yet its specific location and appearance are highly individualized. It is a unique mark defining the center of the anterior abdomen, a scar chronicling the earliest connection to life. Understanding where the umbilicus “should be” involves considering its developmental origin, anatomical position, and aesthetic ideals.
Developmental Origin of the Umbilicus
The umbilicus exists because it was the attachment site for the umbilical cord during fetal development. This cord was a conduit containing two umbilical arteries and one umbilical vein, encased in Wharton’s jelly, and included structures involved in the developing urinary and digestive systems.
At birth, the umbilical cord is cut, leaving a small stump that dries and falls off within a week or two. The resulting umbilicus is essentially a scar, formed by the contraction and healing of the skin and underlying tissues around the umbilical ring. This process completes the closure that began prenatally.
Standard Anatomical Location
For medical and anatomical study, the umbilicus is assigned a standard location, though its exact surface position varies widely among individuals. In a reference anatomical posture, the umbilicus is situated at the level of the interspace between the third and fourth lumbar vertebrae (L3 and L4). This position is used as a landmark for dividing the abdomen into four quadrants for diagnostic purposes.
Another common anatomical reference places the umbilicus approximately halfway along the vertical midline between two bony landmarks. These points are the xiphoid process, the lowest part of the sternum, and the pubic symphysis, the joint at the bottom center of the pelvis. This midline location is central to the “umbilical region” of the abdomen, an area that contains portions of the pancreas, stomach, and major blood vessels.
Factors Affecting Its Final Appearance
The final shape and depth of the umbilicus, such as whether it is an “innie” or an “outie,” is determined by the individual healing process of the umbilical stump. An “innie” results when the skin and scar tissue adhere inward, creating a depression. An “outie” occurs when scar tissue or the umbilical skin protrudes outward, sometimes due to a minor underlying issue like a small umbilical hernia.
The appearance can change throughout a person’s life due to various physiological and physical factors. Significant weight gain or abdominal fat accumulation can alter the shape, sometimes resulting in a deeper, funnel-like appearance. Pregnancy is a common cause for temporary change, as the growing uterus can push a previously inverted umbilicus outward. Surgical procedures, such as abdominoplasty, require the repositioning or reconstruction of the umbilicus, permanently altering its cosmetic look.
The Umbilicus and Human Proportion
Beyond its biological and anatomical location, the umbilicus has historically been considered a reference point for ideal human proportion in art and philosophy. The ancient Roman architect Vitruvius described the navel as the center of the human body, a concept famously illustrated by Leonardo da Vinci in the Vitruvian Man. In this drawing, the umbilicus serves as the geometric center of the circle that circumscribes the figure with outstretched limbs.
While the Vitruvian Man connects the umbilicus to a perfect geometric center, the exact mathematical proportion has been debated. Some theories incorrectly suggest the umbilicus divides the body’s height according to the Golden Ratio (Phi, approximately 1.618). However, the idea of the umbilicus as a harmonic midpoint persists, representing an aesthetic standard that helps define a balanced human form.