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An irregular bone is one that does not have an easily classified shape and defies description. These bones tend to have more complex shapes, like the vertebrae that support the spinal cord and protect it from compressive forces. Many facial bones, particularly the ones containing sinuses, are classified as irregular bones. [1]
It is composed of 270 bones at the time of birth, [2] but later decreases to 206: 80 bones in the axial skeleton and 126 bones in the appendicular skeleton. 172 of 206 bones are part of a pair and the remaining 34 are unpaired. [3] Many small accessory bones, such as sesamoid bones, are not included in this.
Cancellous bone or spongy bone, [12] [11] also known as trabecular bone, is the internal tissue of the skeletal bone and is an open cell porous network that follows the material properties of biofoams. [13] [14] Cancellous bone has a higher surface-area-to-volume ratio than cortical bone and it is less dense. This makes it weaker and more flexible.
The human pelvis exhibits greater sexual dimorphism than other bones, specifically in the size and shape of the pelvic cavity, ilia, greater sciatic notches, and the sub-pubic angle. The Phenice method is commonly used to determine the sex of an unidentified human skeleton by anthropologists with 96% to 100% accuracy in some populations.
The outer surface of the bone, except for the articular surfaces, is covered by the periosteum. [6] Short bones have no clear diaphysis (bone shaft) and metaphysis and have poor vascular supply. [1] [2] Section through the human wrist showing the cancellous bone of the carpals and the absence of diaphysis compared to the long metacarpal bones.
The irregular bones are bones which, from their peculiar form, cannot be grouped as long, short, flat or sesamoid bones.Irregular bones serve various purposes in the body, such as protection of nervous tissue (such as the vertebrae protect the spinal cord), affording multiple anchor points for skeletal muscle attachment (as with the sacrum), and maintaining pharynx and trachea support, and ...
The long bone category includes the femora, tibiae, and fibulae of the legs; the humeri, radii, and ulnae of the arms; metacarpals and metatarsals of the hands and feet, the phalanges of the fingers and toes, and the clavicles or collar bones. The long bones of the human leg comprise nearly half of adult height.
The flat bones are: the occipital, parietal, frontal, nasal, lacrimal, vomer, sternum, ribs, and scapulae. [1] These bones are composed of two thin layers of compact bone enclosing between them a variable quantity of cancellous bone, [1] which is the location of red bone marrow. In an adult, most red blood cells are formed in flat