How Many Bones Does the Human Adult Skeleton Contain?
It is generally said that there are 206 bones in the adult human body, but this is just an average. At birth, there are about 270 bones, and while some fuse together, others grow.
The five bones of the sacrum fuse together to form one bone, and the coccyx (just below the sacrum, including the tailbone) is made up of four or five fused bones. The two pelvic bones that form the os coxae (hips) are really one bone, joined together by the pubic symphysis (immovable cartilage at the pubic bone). However, biologists count these as two bones. Finally there are sesamoid bones, which are bones that form within some tendons as a result of stress.
The axial skeleton is the head and the trunk, or anything other than the appendages. There are about 80 bones in the axial skeleton. There are 22 bones in the skull: eight cranial bones and 14 facial bones. The cranial bones are the frontal, parietal (two), occipital, temporal (two), sphenoid and ethmoid.
The facial bones are maxilla (two), palatine (two), zygomatic (two), lacrimal (two), nasal (two), vomer, inferior nasal conchs (two) and mandible.
The inner ears contribute six bones, or three each. These are called the malleus, incus and stapes--or, in English, hammer, anvil and stirrup.
Underneath the tongue is the hyoid bone. It is often seen damaged in crime scenes when the victim died of strangulation.
The vertebral column and thoracic cage protect the heart, lungs and spinal cord. The vertebral column has 26 bones: seven cervical vertebrae, 12 thoracic vertebrae and five lumbar vertebrae. These are referred to by their numbers: C5, T8, L2, and so on. Below the lumbar vertebrae are the sacrum and coccyx, which are fused bones, but each counts as one.
The thoracic cage has 25 bones: 24 ribs and the sternum. Ribs 8 to 12 are called false ribs. This is because ribs 8 to 10 attach to the cartilage of rib 7, and ribs 11 and 12 are buried in the muscle, and are also called floating ribs.
Pectoral Girdle and Arm
The pectoral girdle consists of two scapulas (shoulder blades) and two clavicles (collar bones). The rest of the upper limb consists of 30 bones each, for a total of 60. Each appendage has the humerus, radius, ulna, eight carpal (wrist) bones, five metacarpals leading to the fingers, and 14 phalanges, or finger joints. Each finger has three phalanges, except for the thumb, which has two.
Pelvic Girdle/Lower Limb
The pelvic girdle is made up of the two os coxae, or hip bones. Each lower limb has 30 bones: the femur, patella, tibia, fibula, seven tarsals (ankle bones, including the heel bone, the calcaneus), five metatarsals and 14 phalanges. As in the hand, the great toe has two phalanges while the other digits have three.
Sesamoid bones often throw off the count of a person's individual bones, because they can appear anywhere. These smooth, round bones often form in the knuckles of the hand. The largest and most well-known of these is the patella, or kneecap, which is formed inside the quadriceps femoris tendon.
Another type of "extra" bone is a sutural bone, which forms between the jagged sutures, or seams, of the cranial bones in the skull. There are also called wormian bones, after Danish physician Ole Worm.
- Anatomy & Physiology: The Unity of Form and Function, 4th edition; Kenneth S. Saladin; 2007