Skeletal System: Types of Bones in the Human Body
Skeletal System - Types of Bones: How to remember the 5 types of bones in the human body! Includes labeled diagrams and examples of long bones, short bones, flat bones, sesamoid bones, and irregular bones!
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Skeletal System
How many bones are in the average adult human body?
There are 206 bones!
The 206 bones make up part of the skeletal system, and they can be categorized into 5 main types based on their shape.
This lecture will teach you the 5 types of bones, and which bones belong in each type, in under 10 minutes with simple memory tricks!
Labeled diagrams and examples are included in the video above!
Types of Bones
The average adult has 206 bones, and they can be categorized into different groups based on their shape.
The 5 main types of bones (and how many) include:
Long Bones (90)
Short Bones (28)
Flat Bones (36)
Sesamoid Bones (4)
Irregular Bones (48)
Note: There is one more category of bones, called sutural bones (Wormian bones).
Sutural bones are small accessory bones sometimes found between cranial sutures.
Not everyone has them, but know they can exist.
Disclaimer: There may be slight variations to how some bones are classified. The exact number of bones for each bone type may vary as a result.
This lecture provides one of the more common ways to classify bones.
1. Long Bones
Long Bones - Quick Notes:
There are 90 long bones (average adult)
Long bones get their name because they are longer than they are wide
Examples:
Bones of the upper extremity (humerus, radius, ulna, etc.)
Bones of the lower extremity (femur, tibia, fibula, etc.)
Clavicles
Trick to Remember Long Bones
L = Long = Limb, CLavicLe (CoLLarbone)
The trick to remember long bones is to use the letter “L” for “Long”.
This will help you remember “L” for “Limbs” and the 2 Ls in “Clavicle”.
Long bones are mainly found in the extremities (limbs).
In fact, most of the bones of the arms and legs are long bones.
You can also use the “L” to remember “Clavicle” or “Collarbone” which contain 2 Ls.
This will help you remember the clavicle (collarbone) is a type of long bone as well.
Simplified: Whenever you think of long bones, think of limbs and clavicle!
Example Long Bones
The average adult has 90 long bones.
Which bones are considered long bones?
Use the memory trick above: “L” for “long” and “limb”
Most long bones can be found in the arms and legs (limbs) including:
Upper Extremity
Humerus (2) - Arm
Radius (2) - Forearm
Ulna (2) - Forearm
Metacarpals (10) - Hand
Phalanges (28) Fingers
Lower Extremity
Femur (2) - Upper Leg
Tibia (2) - Lower Leg
Fibula (2) - Lower Leg
Metatarsals (10) - Foot
Phalanges (28) - Toes
The clavicles are also long bones.
Use the memory trick above: “L” for “long” and the 2 Ls in “clavicle” or “collarbone”
This will help you remember the clavicles or collarbones are also long bones.
Clavicle (2) - Collarbone
2. Short Bones
Short Bones - Quick Notes:
There are 28 short bones (average adult)
Short bones get their name because of their cube-shape
Short bones are about the same length and width
Examples:
Bones of the wrist (scaphoid, lunate, triquetrum, etc.)
Bones of the ankle (talus, navicular, cuboid, etc.)
We reviewed most of the bones in the arms and legs (see above - long bones), except for the bones of the wrist and ankle.
The bones of the wrist and ankle are short bones.
The patella was also skipped, which will be discussed with the sesamoid bones below.
Trick to Remember Short Bones
S = Short = Sprain (Wrist & Ankle)
The trick to remember short bones is to use the letter “S” for “Short” and “Sprain”.
This will help you remember the ankle and wrist, as they are common areas to be sprained.
The short bones are mainly found in the wrists and ankles.
In fact, most of the bones of the wrist and ankle are short bones, except for the pisiform which is a sesamoid bone discussed below.
Simplified: Whenever you think of short bones, think of the wrist and ankle!
Example Short Bones
The average adult has 28 short bones.
Which bones are considered short bones?
Use the memory trick above: “S” for “Short” and “Sprained” to think wrist and ankle.
Short bones are mainly found in the wrist and ankle.
In other words, the carpal bones of the wrist and the tarsal bones of the ankle are short bones.
The carpal bones (wrist) include:
Scaphoid (2)
Lunate (2)
Triquetrum (2)
Hamate (2)
Capitate (2)
Trapezoid (2)
Trapezium (2)
*The pisiform was omitted as it is considered a sesamoid bone - see below!
The tarsal bones (ankle) include:
Talus (2)
Navicular (2)
Cuboid (2)
Calcaneus (2)
Medial Cuneiform (2)
Intermediate Cuneiform (2)
Lateral Cuneiform (2)
Note: The pisiform is considered a sesamoid bone because it develops within a tendon.
There is conflicting information about how to classify sesamoid bones. Some consider sesamoid bones a subtype of short bones. As a result, you may see variations in the total number of short bones in the human body.
This lecture lists 28 short bones, and classifies sesamoid bones separately.
3. Flat Bones
Flat Bones - Quick Notes:
There are 36 flat bones (average adult)
Flat bones get their name for being thin and broad
Flat bones are found in areas where protection of organs is necessary
Examples:
Sternum
Ribs
Bones of the skull (frontal, parietal, nasal, lacrimal, etc.)
Scapula
Trick to Remember Flat Bones
F = Flat = Fort (Rib Cage & Skull/Cranium)
The trick to remember flat bones is to use the letter “F” for “Flat” and “Fort”.
Forts offer protection, and that’s exactly what the flat bones do.
Flat bones are located in areas where protecting vital organs is required, such as the skull and chest/thorax.
Therefore, you can remember flat bones are generally found in the rib cage and part of the cranium or skull.
Simplified: Whenever you think of flat bones, think of the rib cage and skull!
Example Flat Bones
The average adult has 36 flat bones.
Which bones are considered flat bones?
Use the memory trick above: “F” for “Flat” and “Fort” to think areas of protection (skull and rib cage).
Flat bones are located in areas where protecting organs is necessary, such as the skull to protect the brain and the rib cage to protect the heart and lungs.
Flat bones include:
Sternum (1) - Breastbone
Ribs (24)
Skull
Frontal Bone (1)
Parietal Bone (2)
Occipital Bone (1)
Nasal (2)
Lacrimal (2)
Vomer (1)
Scapula (2) - Shoulder Blade
Most of the flat bones of the skull make up the top of the cranium and the midline of the face.
The remainder of the face/skull is made up of irregular bones, which will be discussed below.
The scapula is also considered a type of flat bone, which can be remembered because it is close to the rib cage.
4. Sesamoid Bones
Sesamoid Bones - Quick Notes:
There are 4 sesamoid bones (average adult)
Sesamoid bones get their name for resembling a sesame seed
Sesamoid bones are pea-shaped bones within tendons
Examples:
Pisiform (carpal bone)
Patella (kneecap)
Trick to Remember Sesamoid Bones
S = Sesamoid = Sesame Seed Shaped (Pisiform & Patella)
Pea-Shaped = Pisiform & Patella
There are 2 tricks to remember sesamoid bones.
The first trick is to use the beginning of the word “sesamoid” to remember “sesame seeds”, or use the “S” in “Sesamoid” to remember “Sesame Seed Shaped”.
This will help you remember the seed-shaped pisiform and patella bones.
The second trick is to think of sesamoid bones as being pea-shaped.
Coincidentally, “Pisiform” and “Patella” both start with the letter “P” (Pea).
Simplified: Whenever you think of sesamoid bones, think of the pisiform and patella!
Example Sesamoid Bones
The average adult has 4 sesamoid bones.
Which bones are considered sesamoid bones?
Use the memory trick above: “S” for “Sesamoid” and “Sesame Seed Shaped”, or think “Pea”-shaped (letter P) to remember pisiform and patella.
As previously mentioned, sesamoid bones get their name for resembling a sesame seed.
The sesamoid bones are the sesame seed or pea-shaped bones within tendons, and they include:
Pisiform (2) - Carpal Bone
Patella (2) - Kneecap
The pisiform is in the flexor carpi ulnaris tendon.
The patella is in the quadriceps tendon, and it provides an attachment point for the patellar tendon.
The pisiform is 1 of the 8 carpal bones in the wrist.
The patella is the kneecap.
Therefore, the average adult has 4 sesamoid bones.
Note: Nearly everyone has 2 patellae and 2 pisiform bones, which is why they are included in the 206 bones.
However, some people may have additional sesamoid bones in tendons near the joints of their hands or ankles.
5. Irregular Bones
Irregular Bones - Quick Notes:
There are 48 irregular bones (average adult)
Irregular bones get their name for their odd shapes
Irregular bones do not fit the other categories of long, short, flat, or sesamoid
Examples:
Hip bones
Vertebral column (cervical, thoracic, lumbar, etc.)
Hyoid bone
Bones of the skull (temporal, ethmoid, sphenoid, etc.)
Ear ossicles (malleus, incus, and stapes)
Trick to Remember Irregular Bones
I = Irregular = I-Shaped (Hips, Vertebrae, Skull, Ears)
The trick to remember irregular bones is to use the letter “I” for “Irregular” to think “I-shaped”.
The irregular bones collectively make the shape of an “I”.
What do we mean by that? Here’s the trick!
The irregular bones are mainly found in the ears, skull, spine, and hips.
Collectively, these bones make the shape of a capital “I”.
The ears and skull form the top horizontal line of the letter “I”.
The vertebrae form the vertical line of the letter “I”.
The hips form the bottom horizontal line of the letter “I”.
This will help you remember the overall location of the irregular bones.
Simplified: Whenever you think of irregular bones, think of the ear, skull, vertebrae, and hips!
Example Irregular Bones
The average adult has 48 irregular bones.
Which bones are considered irregular bones?
Use the memory trick above: “I” for “Irregular” and “I-shaped” to think of the collectively I-shaped location of the ears, skull, vertebrae, and hip bones.
As previously mentioned, irregular bones are primarily found in the hips, spine, parts of the skull, and ears.
Collectively, they form the shape of an “I” which can help you remember the overall location of the irregular bones.
Irregular bones include:
Hip Bones (2)
Vertebral Column
Cervical (7)
Thoracic (12)
Lumbar (5)
Sacrum (1)
Coccyx (1)
Hyoid Bone (1)
Skull
Temporal Bone (2)
Ethmoid (1)
Sphenoid (1)
Zygomatic (2)
Maxilla (2)
Mandible (1)
Inferior Nasal Concha (2)
Palatine (2)
Ear Ossicles
Malleus (2)
Incus (2)
Stapes (2)
Note: The number of vertebrae listed above is for an adult.
Most individuals are born with 33 vertebrae (7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal).
The 5 sacral and 4 coccygeal vertebrae fuse by adulthood to form the sacrum and coccyx respectively.
The skull contains irregular bones, in addition to the flat bones discussed above.
The irregular bones of the skull make up much of the face, whereas the flat bones form the top of the cranium to protect the brain.
Reminder: Flat bones help protect vital organs.
Note: There may be slight variations to how some bones are specifically classified. This lecture provides an overall understanding of the different types of bones.
Types of Bones - Summary
You learned the 5 major types of bones, along with examples and memory tricks to remember them.
1. Long Bones:
Think limbs and clavicle (collarbone).
L = Long = Limb, CLavicLe (CoLLarbone)
This will help you remember the long bones include most of the bones of the arms and legs (limbs), as well as the clavicle.
2. Short Bones:
Remember sprain.
S = Short = Sprain (Wrist & Ankle)
This will help you think of the ankle and wrist, as they are commonly sprained.
The short bones include the bones of the ankle (tarsals) and wrist (carpals).
3. Flat Bones:
Think of a fort.
F = Flat = Fort (Rib Cage & Skull/Cranium)
Forts help to provide protection.
This will help you remember the flat bones include the sternum, rib cage, scapula, and part of the skull, which help protect vital organs such as the heart, lungs, and brain.
4. Sesamoid Bones:
Think sesame seed-shaped or pea-shaped.
S = Sesamoid = Sesame Seed Shaped (Pisiform & Patella)
Pea-Shaped = Pisiform & Patella
This will help you remember the sesame seed or pea-shaped pisiform and patella.
5. Irregular Bones:
Remember how they collectively form the shape of an “I”.
I = Irregular = I-Shaped (Hips, Vertebrae, Skull, Ears)
This will help you remember the overall location of the irregular bones including the hip bones, vertebrae, part of the skull, and ears.
References
https://www.visiblebody.com/learn/skeleton/types-of-bones
https://www.kenhub.com/en/library/anatomy/bones