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|
|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|
Excerpted from The Complete Idiot's Guide to Anatomy and Physiology 2004 by Michael J. Vieira Lazaroff. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.