Anatomy and Physiology: That's the Long and Short of It

That's the Long and Short of It

A lot of school kids learn that they have 206 bones, but most never learn that number of bones may vary from person to person! The troublemakers are two types of bones that grow in unusual places, as a result of our development. One type is called sesamoid, because they are flat, and usually small, bones shaped like sesame seeds; sesamoid bones develop in tendons around the hands, feet, and knees (in all, a total of 26 locations). The number of these varies, but we all have a pair in our knees: the kneecaps, or patellae.

The other type is called sutural bones (or wormian bones), because they form in the connective tissue when cranial bones form sutures. These bones form as little islands in the developing sutures. A quick look at a suture on a real skull (rather than a model) often reveals multiple small wormian bones. The rest of the more “garden variety” bones are listed in the following table (and in Figure 5.3).

The Four Major Bone Types
Bone Type	Description	Location
Long	Long, slender	Arms, legs, phalanges
Short	Short, box-like	Carpals, tarsals
Flat	Thin, parallel surfaces	Skull, ribs, scapulae
Irregular	Complex, with projections	Vertebrae and skull