Skeletal System Part 2


The Skeletal System is a framework consisting of bones and other connective tissues, which protects and supports the body tissues and internal organs.


The human skeleton contains 206 bones, six of which are the tiny bones of the middle ear (three in each ear) that function in hearing.

Let's take a closer look at the Appendicular bones...

And now a closer look at the Axial bones...

Starting from the top, we have the cranium.  You may have thought that your head was one bone, but actually, it is made up of a number of bones that have fused together.

The ribs and vertebrae are numbered (from the top down) to identify them.  Notice that there are a couple of different types of ribs, and takenote of how they differ.

There are Five types of bones...


Much longer than they are wide

Humerus (2)

Radius (2)

Ulna (2)

Metacarpals (10)

Phalanges of the hand (28)

Femur (2)

Tibia (2)

Fibia (2)

Metatarsals (10)

Phalanges of the foot (28)

Clavicles (2)

Consists of a shaft plus 2 expanded ends.


Roughly cube shaped

Carpal Bones

Tarsal Bones



















Thin, flattened, and usually a bit curved

Cranial Bones (4) (most bones of the Skull)

Thorasic Cage Bones (25) (Scapulae, Sternum & Ribs)




Round… resembling a sesame seed

Short or irregular bones imbedded in a tendon.

Patella (largest of the sesamoid bones and only
one considered part of the 206)


Complex in design and do not fall into any other category

Vertebrae Column (26)

Scapulae (2)

Patella (2) (Knee Cap)

Skull (25) (Spehnoid & Ethmoid)

Coxal (2)

Bone Tissue

Bone Tissue comes in two distinct types:


  1. Spongy Bone - Made up of small,  needle-like pieces of bone, with many open spaces.

  2. Compact Bone - homogeneous, with no open spaces -  solid and heavy.

Gross Anatomy of Long Bones

A. Diaphysis

Shaft or center of the bone

Composed of compact bone

Has a Central Cavity (Medulla)


  • Outside covering of the diaphysis

  • Fibrous connective tissue membrane

Sharpey’s fibers

  • Secure periosteum to underlying bone


  • Supply bone cells with nutrients




Adults:   yellow marrow

                (mostly fat)

Infants: red marrow

                (blood cell formation) 
Adults:   red marrow

                is found in flat bones &

                epiphyses of long bones

B. Epiphysis

  • Ends or caps of long bones

  • Mostly spongy bone

  • Epiphyseal plates allow for growth of long bone during childhood

    • New cartilage continuously forms

    • Older cartilage ossifies
      (turns to bone)

    • Cartilage breaks down, & bone replaces cartilage

Articular Cartilage

  • Covers the external surface of the epiphyses, where two bones meet

  • Made of hyaline cartilage

  • Decreases friction at joint surfaces & allows joints to slide over each other

Skeletal Development

  • In embryos, the skeleton is primarily hyaline cartilage

  • During development, much of this cartilage is replaced by bone

  • Cartilage remains in adults in isolated areas

    • Bridge of the nose

    • Parts of ribs

    • Joints

  • Bones are remodeled and lengthened until growth stops

  • Bones change shape somewhat

  • Bones grow in width

  • Bones fuse together as children grow

  • Children have about 100 more bones than adults

Childs Sacrum, showing bones prior to fusing

Compare to adult Sacrum, after bones fuse.

How can you tell the sex of a skeleton?

You've seen the TV show or movie where forensic scientists identify the age and sex of a victim from nothing more than some bones.  Scientists can know this information by taking a close look at a skeleton.  In an adult, the long bone have stopped growing, while youngsters still show activity at the Epiphyseal plates.


Sex can be determined by the shape and bones of the Pelvis ( the Pelvic Bone, Sacrum, and Coccyx).  Female bones have different shape so that their pelvis can handle childbirth.

Males: thicker and heavier skull, more prominent forehead

Females: sharper ridges on orbit, rounder jaw

Movement (Articulation)

  • Articulations (“connecting”) of bones

  • Structurally

    • Fibrous joints

      • Generally immovable

      • Bones united by fibrous tissue 

      • Synarthrosis Joints

        • Examples

          • sutures of skull

    • Cartilaginous joints

      • Immovable or slightly moveable

      • Bones connected by cartilage

      • Amphiarthrosis Joints

        • Examples

          • Pubic symphysis

          • Intervertebral joints

    • Synovial joints

      • Freely moveable

      • Articulating bones are separated by a joint cavity

      • Synovial fluid is found in the joint cavity

      • Diathrosis Joints

      • Articular cartilage (hyaline cartilage) covers the ends of bones

      • Have a joint cavity filled with synovial fluid

      • Ligaments reinforce the joint

        • Examples

          • hip

          • elbow

  • Purpose of Joints

    • Hold bones together

    • Allow for mobility


The ways joints are classified

  • Functionally

    • Synarthroses

      • Immovable

    • Amphiarthroses

      • Slightly moveable

    • Diarthroses

      • Freely moveable

Synarthroses - Immoveable joints

Diarthroses -

Freely moveable joints

Amphiarthroses - Slightly moveable joints

Types of Synovial Joints (based on shape)

The six types of Synovial Joints:

a. Gliding Joint

b. Hinge Joint

c. Pivot Joint

d. Condyloid Joint

e. Saddle Joint

f. Ball-and-socket Joint