By Elizabeth A. Murray, Mount St. Joseph University
Do you have any idea how many bones there are in the human body? If you have studied anatomy and physiology in the past, the number 206 might come to mind. But do you know that’s actually an average among humans—and only adult humans? The number actually varies with age.
Ossification
There’s a general pattern of growth and development in which the skeleton starts as other types of connective tissue, including cartilage. Then, throughout our prenatal and postnatal development, some of that cartilage begins to ossify, which means it transitions to bone.
And a typical long bone—like the humerus of the upper arm or femur of the thigh—doesn’t just ossify in a single bony element. First, the shaft, called the diaphysis in anatomy, starts turning into bone, becoming what’s known as the bone’s primary center of ossification.
Then, the two ends, called epiphyses, turn to bone, becoming secondary ossification centers. This process leaves bridges of cartilage between the shaft and its two ends. These are the bone’s growth plates; they are the regions where the bone continues to grow in length during childhood.
Eventually, when the bone has achieved its genetically programmed length—provided good health and nutrition—the growth plates close up, fusing the diaphysis to the epiphyses and resulting in a single bone. Long bones of the body grow that way; the skull and other types of bones form from other soft tissues in different patterns of ossification.
Bone Count of a Fetus
When these long bones are developing and still composed of multiple different bony elements, technically we actually have far more than 206 bones.
In the third trimester of fetal life, if all ossification centers are counted, at the highest point the number is about 800 tiny “bones”— they would be better described as 800 separate ossification centers, or bits of bone in formation. Some of these bony elements fuse together in utero, resulting in about 450 “bones” at birth—but sources vary on the exact numbers.
Number of Bones in Adults
In fact, over anatomical history, sources have varied significantly even in the total bone count in the adult skeleton. The total attributed from Galen’s work was 248, whereas Vesalius counted 307, and the modern number is 206. It wasn’t that the number changed through the past few thousand years but depended on how they counted—like counting the sternum as one bone or two.
But even after the adult skeleton is formed, and the last growth region at the medial end of the clavicle closes, the number of bones can still change. For instance, arthritis can fuse vertebrae, the 22 bones in the skull often fuse together in old age, and arthritis or injury can fuse small elements like finger and toe bones. So, technically once that happens, an individual doesn’t really have 206 separate bones anymore.
This article comes directly from content in the video series How We Move: The Gross Anatomy of Motion. Watch it now, on Wondrium.
Bones as Identification Factors
Still, aside from the changes that occur with age, 206 is an average number of bones in the normal adult. Individuals can be born with extra bones or fewer bones; it can be seen in forensic work, and it’s not even all that rare— because unusual skeletal features can help get a person identified. For example, we may suspect who the person is from other clues—like an ID card, or simply the location where they’re found.
And if we can find an x-ray of that suspected person that includes the unusual feature seen in the morgue, we can match those up and get a head start on identification, long before the DNA results are back.
Bone Anomalies
In fact, for any given anatomical feature, there’s what is called the 70% rule: It’s estimated that only 70% of us have the by-the-book pattern for a given structure, meaning that 30% of people have anomalies. So, if 100 people are watching this course now, that means that around 70 of them have 206 bones, and 30 of them probably have some variation in bone number—and not just from age or maybe an injury that fused bones, but congenitally, from their own genetics and development.
And when you consider how many different anatomical structures we each have, and that approximately 30% of us have anomalies for each one of those, it’s no wonder we see so much diversity in ourselves and in each other. Indeed an exciting and amazing fact—both to think about and to see!
Symmetry and Repetition in Bones
For one thing, there are a lot of repeating themes in the body, like 24 individual vertebrae within the spine, which have many similar features, and 12 pairs of ribs, that likewise have much in common with each other. And there are 56 bones called phalanges that make up our fingers and toes and have great similarities, and those 56 are over a fourth of the typical 206 bones right there.
We also have bilateral symmetry in our favor, so because the right and left sides of the body are basically mirror images, once you know about one side, you’ve known the other side, too. Finally, due to our four-limbed, tetrapod ancestry, the upper limb and lower limb have much in common, as we will see.
Common Questions about How Many Bones Human Beings Have
Long bones do not ossify in a single bony element. First, the shaft, called the diaphysis in anatomy, starts turning into bone, becoming what’s known as the bone’s primary center of ossification. hen, the two ends, called epiphyses, turn to bone, becoming secondary ossification centers.
In the third trimester of fetal life, if all ossification centers are counted, at the highest point the number is about 800 tiny “bones’ or ossification centers, or bits of bone in formation. Some of these bony elements fuse together in utero, resulting in about 450 “bones” at birth—but sources vary on the exact numbers.
Over anatomical history, sources have varied significantly even in the total bone count in the adult skeleton. The total attributed from Galen’s work was 248, whereas Vesalius counted 307, and the modern number is 206.
