HUMAN SKELETON

First let us understand more about the human skeleton as it forms the framework of human body about which all organs and systems function and perform.

The human skeleton is made of bones, some of them joined together, supported and supplemented by a structure of ligaments, tendons, muscles, and cartilage.

The skeleton changes composition over a lifespan. Early in gestation, a fetus has no hard skeleton — bones form gradually during nine months in the womb. When a baby is born it has more bones than it will as an adult. On average, an adult human has 206 bones in their skeleton (the number can vary slightly from individual to individual), but a baby is born with approximately 270. The difference comes from a number of small bones that fuse together during growth. These include the bones in the skull and the spine. The sacrum (the bone at the base of the spine) consists of six bones, which are separated at birth but fuse together into a solid structure in later years.

There are 6 bones (three on each side) in the middle ear that articulate only with themselves, and one bone, the hyoid bone, which does not touch any other bones in the body.

The longest bone in the body is the femur and the smallest is the stapes bone in the middle ear.

Fig: Human Skeleton

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Function

The skeleton functions not only as the support for the body but also in hematopoiesis, the manufacture of blood cells that takes place in bone marrow (which is why bone marrow cancer is very often a terminal disease). It is also necessary for protection of vital organs and is needed by the muscles for movement. Not only does the skeleton serve to help manufacture blood cells, but it also serves as a mineral storage deposit in which nutrients can be stored and retrieved.

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Organization

One way to group the bones of the human skeleton is to divide them into two groups, namely the axial skeleton and the appendicular skeleton. The axial skeleton consists of bones in the midline and includes all the bones of the head and neck, the vertebrae, ribs and sternum. The appendicular skeleton consists of the clavicles, scapulae, bones of the upper limb, bones of the pelvis and bones of the lower limb.

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Gender differences

There are many differences between the male and female human skeletons. Men tend to have slightly thicker and longer limbs and digit bones while women tend to have larger pelvic bones in relation to body size. Women also tend to have narrower rib cages, smaller teeth, less angular mandibles, and less pronounced cranial features such as the brow ridges and occipital protuberance (the small bump in the cranium's posterior). Most striking is the difference in hip bones owing to differences related to the process of reproduction, and very likely also to the biological process of sexual selection. There are also a number of smaller differences between human male and female skeletons.

Chapter III - Human Anatomy