There are four body bone types: short, flat, long, and irregular. The irregular bones of the human body are the vertebrae, sacrum, coccyx, maxilla, mandible, temporal, sphenoid, ethmoid, zygomatic, palatine, inferior nasal concha, and hyoid.
Types of Bone
The human skeleton is made up of bones of all shapes and sizes. There are some tiny ones, such as the inner ear bones, and some large ones, like the bones in your arms and legs.
Bones that are longer than they are wide are called long bones. They consist of a long section of bone with two thicker ends. They are mostly composed of compact bone but may have a large amount of spongy bone around the ends. Long bones can be found in the thigh, arm, leg, and forearm.
In contrast, there are also plenty of short bones. These bones are called ‘short’ because they are about as long as they are tall. Because of this, they tend to look almost cuboid. They are mostly made of spongy bone with a thin layer of compact bone for stability. You can find short bones in your wrist and your ankle.
Flat bones are thin, balanced, and usually curvy in shape. For example, you can find curved bones in your skull.
That brings us to irregular bones. Irregular bones are grouped only because they don’t fit into the abovementioned three categories. They do, however, have some similarities. For example, they are usually made up of spongy bone and a thin layer of compact bone, just like short bones. Before we look at the different kinds of irregular bones’ functions within the skeleton, we need to look at the materials bone is made up of.
What is compact bone? What is spongy bone?
Bone is made up of several different layers and materials.
- The top layer of bone is called the periosteum. This is a membranous tissue that covers the surface of bones. It’s very important for repairing and growing them.
- Next up, there’s compact (or hard) bone. This layer is heavy and very dense. It gives the bone strength. This is the part you see when you’re looking at a skeleton.
- There’s also spongy (or cancellous) bone. There are lots and lots of layers of this spongy bone. The spaces in the cancellous bone are full of blood vessels and bone marrow. Red blood cells, some white blood cells, and platelets are made here. Bone marrow is thick and jelly-like, and its job is to make blood cells.
- Bones are made out of a protein called collagen. A mineral called calcium phosphate makes the framework of the bones hard and strong. Bones store calcium and release some into your blood if other body parts need it.
Irregular bones: Function and Facts
The Spine
Your spine, or spinal column, comprises a set of irregular bones called vertebrae. There are 33 in total! Your spine holds you upright when you’re standing or sitting and lets you twist and bend.
The spine protects the spinal cord. This big bundle of nerves sends information from your brain to the rest of your body.
The Sacrum
This is a large bone at the bottom of your spine. It’s almost triangular. This bone strengthens your pelvis, making it more stable. It also protects your bladder and intestines.
The Coccyx
The coccyx is often referred to as the tailbone. Humans had a tail a long, long time ago. Even though we no longer have seats, the coccyx still has a job. This bone is an attachment point for tendons, ligaments, and muscles like the gluteus maximus.
Irregular Bones of the Skull
The human skull is made up of 22 different bones. These bones work together to protect the brain and support your face. But, did you know that the biggest ‘Homo skull ever found is the skull of a species that researchers named Homo long, or ‘dragon man’? The skull was found in Northern China and measures 23 centimeters long and more than 15 centimeters wide! It is believed the owner of this skull lived between 146,000 and 296,000 years ago.
Now, let’s find out more about the irregular bones’ function as a part of the skull:
The Temporal Bone
These bones are found at the base and the sides of the skull. The temporal bone is made up of four parts. These are named the squamous, mastoid, petrous, and tympanic parts. They are underneath your temples and contain the insides of your ears.
The Sphenoid
This is another bone that makes up part of your skull. It can be found in the middle of the head, towards the front. The bone looks a little bit like a pair of wings. It is one of the seven bones that make up the orbit or eye socket.
The Ethmoid
The ethmoid is also an unpaired bone in the skull. It separates the nasal cavity from the brain and can be found at the roof of the nose, between the orbits or eye sockets.
The Zygomatic Bone
This bone is more commonly known as the cheekbone. It connects and articulates with the maxilla, sphenoid, frontal, and temporal bones.
The Maxilla and the Mandible
The maxilla is the upper, fixed part of your jaw. The mandible is the lower part of the jaw. You can only move the mandible used when speaking and chewing. Your teeth sit in the maxilla and the mandible: your top teeth are in the maxilla, and your bottom or lower teeth are in the mandible. The word “mandible” comes from the Latin mandibula, which means ‘jawbone’ or ‘one used for chewing.’
The Palatine Bones
These bones are located above the uvula in the throat. They make up the hard palate with the maxilla. This bone has an opening for arteries so that blood can flow around that area of the body around the nasal cavity.
Inferior nasal concha
This is one of the three nasal conchae in the nose. It extends along the wall of the nasal cavity and is made of spongy bone curled up like a scroll. These three nasal bones are lined with mucus, so when air passes through the nasal cavity, it is warmed, moistened, and cleaned.
The Hyoid Bone
The hyoid bone is a horseshoe-shaped bone between the chin and the neck. It is the only bone in the human body that is not connected to any other bones nearby. This bone provides attachment to the muscles of the tongue, larynx, epiglottis, pharynx, and the floor of the mouth.
