Irregular bones include vertebrae in the back, carpals in the hand, tarsals of the feet and the patella in the kneecap, according to MedicineNet. Irregular bones are normally compact and have different sizes and shapes than other bones in the human body.
Irregular bones don't fall into the other categories of bones, notes Teach PE. The sacrum at the base of the spine and the mandible in the lower jaw are examples of irregular bones because they have non-uniform shapes. These types of bones have softer, spongy bone surrounded by a thin, compact layer of outer bone.
For example, vertebrae are 24 bones stacked vertically from the base of the skull down to the pelvis near the hips. The spine provides structure for other bones and allows fluids to move freely through the body. Nearly 80 percent of the load of the spine is placed on the vertebral body, which serves as hard bones in between the softer discs of the spine, according to Cedars-Sinai. Vertebrae surround the spinal column to protect important portions of the nervous system.
The four types of bones in the human body are long bones, short bones, flat bones and irregular bones. Long bones include arm bones and leg bones. Short bones are the collar bone and some bones of the hands and feet. Flat bones have thin, broad surfaces such as the ribs, breastbone and wingbone, notes MedicineNet.