Bone Anatomy

Bone Features - Shape

The 206* bones found in the adult skeleton are classified according to the shapes described in Table 1:

 

Shape Features Example(s) Interesting Fact
Long

Longer than they are wide.

Grow mainly be elongation of the diaphysis.

Femur, humerus.

Metacarpals and metatarsals - "short" relative to other "long" bones but still longer than their width!

The femur, the long bone of the thigh, is the heaviest bone in the body.
Short

Small, box-shaped. 

About as long as they are wide.
Carpals and tarsals (found in the wrist and ankle respectively) There are 8 of these in the wrist and 7 in the foot.
Flat

Thin surface.

Provide protection for underlying tissues.

Ribs, scapula, sternum, roof of skull. There are actually 6 flat bones in the skull - the frontal, temporal, parietal, vomer, nasal and lacrimal bones.
Sutural    

Small, flat and irregular

Like a jigsaw puzzle; fit between flat bones of skull.

Form the sutures of the skull including the lambdoidal, coronal and squamosal sutures. Some are as small as a grain of sand!
Irregular Surfaces may be notched, ridged, short or flat. Pelvis (coxae), spinal vertebrae. The hyoid bone, situated between the chin and thryroid cartilage, is an irregular bone only anchored in place by muscles.
Sesamoid

Small, flat

Develop inside tendons

"Sesame-seed shaped"

Sesamoid patellae ("knee-caps") * There are discrepancies between individuals in the number of their sesamoid bones.  They may form in at least 26 locations and are the main reason why the commonly quoted figure of 206 as the numebr of bones in the adult skeleton is only usually approximate.

Table 1: The shapes that bones of the adult skeleton can be classified as.

Bone Markings

The surface features shown in Table 2 all appear on the bones shown in Figures 1 - 6 of the Gross Anatomy page.

 

Anatomical Term Definition
Head The expanded articular end of an epiphysis.
Neck Separates the head from the shaft. 
Trochanter A large, rough projection
Tuberosity A smaller (than trochanter), rough projection
Tubercle A small, rounded projection.
Condyle A smooth, rounded articular process
Facet A small, flat articular surface.
Foramen A round passageway for blood vessels /  nerves.
Spine A pointed process, to which muscles often attach or other bones articulate with.
Trochlea A grooved articular process shaped like a pulley.

Table 2: Some definitions of surface features seen on many bones.  Adapted from Table 6-1 of Fundamentals of Anatomy and Physiology (see References at end of Internal Bone Structure).

External Bone Structure

A long bone (Figure 1) shows the three main regions of bones:

  • The diaphysis, the long tube-shaped shaft. 
  • The epiphysis, the expanded area at each end of the bone.
  • The metaphysis, the narrow region connecting the diaphysis to the epiphysis at each end.

Diagram showing main features of a long bone

Figure 1: The structure of a long bone.  Courtesy of Wikimedia Commons (http://en.wikipedia.org/wiki/File:Illu_long_bone.jpg)

Some of the internal structures also shown in Figure 1 are described in Internal bone structure

 

Continue to The Human Skeleton.