The adult human body contains 206 bones. For ease of reference, anatomists separate these into two divisions: the axial skeleton, which contains the bones along the long axis of the body (i.e., the head and the torso) and the appendicular skeleton, which includes the bones of the appendages. 172 of the 206 human bones are part of a pair, including all 126 bones of the appendicular skeleton and 46 of the 80 bones in the axial skeleton. The 34 unpaired bones include six skull bones, 26 vertebrae, the sternum of the chest and the hyoid under the chin.
While it is rarely necessary to remember all 206 bones of the body by name, you may be required to learn all of the bones in a group, such as the bones of the lower extremity or the pelvis, and how they relate to each other in physical space. Mnemonics, be they your own or ones you find online, are a great learning aid in this realm.
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The adult human body contains 206 bones. Anatomists separate these into two divisions: the axial skeleton, which contains the bones along the long axis of the body (i.e., the head and the torso) and the appendicular skeleton, which includes the bones of the appendages.
Basics of Bones in the Body
Bones are the main component of the skeletal system, which also includes cartilage, ligaments, tendons and joints. The skeletal system supports and protects the body's organs, allows locomotion by providing attachment and anchor points for muscles, synthesizes blood cells and serves as a storage depot for minerals and fat.
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That bones serve as a scaffolding to give animals shape and structure, playing the same basic role as beams do in buildings, is the most obvious of the functions they serve. It is also fairly obvious that they are exquisitely protective. People usually learn at a young age that their brain, heart, lungs and spinal cord are absolutely necessary for survival; it comes as no surprise that these organs enjoy an unusually thick and elaborate level of bony armor.
The other jobs bones do are less well known to lay people than the structural and protective roles. Bones contain a yellowish substance called marrow, and it is here that blood cells – red blood cells, white blood cells and platelets – are made. The fat cells in marrow can be released into the bloodstream for use elsewhere, as can some of the minerals (mostly calcium and phosphorus) stored in the hard matrix of bone tissue itself.
Components of the Skeleton
As mentioned, the adult skeleton includes a total of 206 bones, 80 of them in the axial skeleton and 126 in the appendicular skeleton. The hands and feet alone include 106 of the 126 appendicular bones, attesting to the evolutionary demand for locomotion and finely controlled limb movements.
The axial skeleton includes the bones of the head, neck, chest and back. The skull contains 28 bones, 22 of which are members of paired sets and six of which are unpaired. As you may have gathered from knowing that the body in general is symmetrical, the six unpaired skull bones span the midline of the body, extending equally to either side of it (an example is the mandible, or lower jaw).
The vertebral column consists of 26 bones, 24 of which are genuine vertebrae (from top to bottom: seven cervical, 12 thoracic and five lumbar) and the remaining two being the sacrum and coccyx (tail bone). The main task of the vertebral column is to protect the spinal cord. Humans also have 12 pairs of ribs, which guard the vital organs of the thorax. The sternum (breast bone) serves as the point of attachment of the ribs in front and is also protective, while the hyoid bone "floats" in front of the windpipe under the mandible, joined only to connective tissue rather than other bones.
Over 80 percent of the bones of the appendicular skeleton are in the hands (27 bones each) and the feet (26 bones apiece). Each hand and each foot consists of five short bones, called metacarpals in the hands and metatarsals in the feet, that connect to the 14 phalanges that make up the fingers or toes (two in each thumb and toe, and three each in the remaining four digits of each appendage). The hands include eight wrist bones (carpals) and the feet have seven ankle bones (tarsals).
The upper body contains five paired bones in the shoulder and arm. From the midline outward, these are the scapulae (shoulder blades), clavicle (collar bone), humerus (upper arm), and ulna and radius (forearm). The lower body also contains five paired bones in the pelvis and leg, including the hip (in turn consisting of the fused ilium, ischium and pubis), femur (thigh bone), patella (knee cap), and tibia and fibula (shin bones).
Groups of bones, especially the more obscure ones, may be more easily remembered with the help of literary devices called mnemonics, which are usually sayings in which the first letter of each word in the saying matches the first letter in the list of objects being memorized.
For example, you might more easily commit to memory the names of the six unpaired skull bones by coming up with a clever phrase that incorporates their first letters. Ideally, these would be in a meaningful physical order as well. For example, Napa Valley College offers "Fraternity Parties Occasionally Teach Spam Etiquette" to help you recall the names of frontal, parietal, occipital, temporal, sphenoid and ethmoid bones. The eight paired bones of the face lend themselves to similar gamesmanship, again from Napa Valley College; "Virgil Can Not Make My Pet Zebra Laugh" is one of countless ways to remember vomer, conchae, nasal, maxilla, mandible, palatine, zygomatic and lacrima. (You'll need to study a diagram of the skull to appreciate why this order makes sense, though it's not the only order that does so.)
The eight wrist bones – from the row of four nearest the shoulder to the row of four adjoining the metacarpals, from the outside to the inside of each row – are the scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate and hamate ("Stop Letting Those People Touch The Cadaver's Hand"). Similarly, the seven ankle bones – from the shin outward, the talus, calcaneus, navicular, medial cuneiform, intermediate cuneiform, lateral cuneifrom and cuboid – can be memorized via the phrase "Tall Californian Navy Medical Interns Like Candy," or the like.
Early Development of the Skeleton
Multiple bones of the skull are among the many bones in the body that fuse after birth, lowering the ultimate total to the widely cited 206 figure. The main reason the skull does not form fully during fetal development is that some flexibility of the skull bones is required for the head to pass through the birth canal without undue trauma to either the brain or the body of the mother. Human baby brains are unusually large by mammalian standards, so some sort of compromise during pregnancy and labor is necessary. The soft spots you may have tenderly felt on the head of an infant sibling are called fontanelles. These consist of fibrous connective tissue to allow for further growth of the brain as the infant develops into a child and then into an adult.
Sometimes, in about 1 in every 2,000 births and more commonly in boys, the sutures between skull bones become prematurely fused. This condition, called craniosynostosis, can fortunately be treated with surgery shortly after birth to allow for normal brain development and comparatively normal skull maturation as well.