The Skeletal Plan

The human skeleton is composed of 206 bones. These bones are arranged in two groups: the axial skeleton which is composed of the central bones of the body (skull, hyoid, ribs, sternum, and vertebral column) and the appendicular skeleton which contains the bones of the shoulder and pelvic girdles and of the arms and legs.

All bones can be grouped according to their shape: long, short, flat, and irregular, or according to their location: su-tural and sesamoid. Sutural bones are located between the bones of the skull. They do not occur in all individuals. Sesamoid bones are bones located within tendons. Everyone has at least two sesamoid bones, the patellas (kneecaps).

Every bone contains both compact and cancellous osseous tissue. The compact tissue provides strength and support. The cancellous tissue makes the bone light weight without sacrificing strength. Cancellous bone also provides a site for blood cell production. The substance in the cavities of cancellous bone is called red marrow because of its red color.

To further reduce the weight of the skeleton, long bones contain a central cavity, the medullary cavity. The cavity serves as a storage site for adipose tissue (yellow marrow). Lining the medullary cavity is the endosteum (endo = Gr. inside).

The proximal and distal ends of long bones are termed the epiphyses (sing. - epiphysis). The epiphyses are covered with articular cartilage (arthros = Gr. joint). The term "articular" refers to its function (physiology). Anatomically this tissue is hyaline cartilage. The shaft of the bone is the diaphysis. Between the diaphysis and the epiphyses can be seen the epiphyseal lines, which are the remnants of the growth zones from childhood.

A break in a bone is called a fracture. Several terms are used to describe fractures and the procedures used to correct them. If the skin is broken open, the fracture is termed a compound or open fracture. If the skin remains intact, it is a simple or closed fracture. The procedure used to repair a fracture by manipulation is closed reduction. If surgery is required to restore the bone, then the process is termed open reduction.

A greenstick fracture is one in which the bone is broken only on one side. Another type of incomplete fracture is the fissured fracture in which the bone is partially split linearly.

Complete fractures can be transverse, oblique, or spiral. If a piece of bone is broken out of the diaphysis, the fracture is segmental. If many pieces are broken out then the fracture is comminuted. When one bone is jammed into another the fracture is compacted.

Exercise 8.1

Using your textbook as a guide, label the figure of the humerus, a representative long bone.

Exercise 8.2

Label the bones and regions of the skeleton shown in Figure 8.2.

Exercise 8.3

Using your textbook as a guide, label the fractures shown in Figure 8.3-

(type of bone)

(type of marrow)

(type of bone)

Skeletal Bones Labeling

Figure 8.1 Humerus, A Long Bone

Articular cartilage Cancellous bone Compact bone Diaphysis Endosteum Epiphysis Medullary cavity Metaphysis Periosteum Red marrow Yellow marrow

Muscles That Attach The Coxae
Figure 8.2 Skeletal System

Appendicular skeleton Axial skeleton Femur Fibula Humerus Hyoid Os coxa Patella Radius Rib Skull Sternum Tibia Ulna Vertebral column

Figure 8.3 Bone Fractures

Colles' Comminuted Compacted (impacted) Fissured Greenstick Oblique Segmental Spiral Transverse

The surfaces of bones have various structural features called bone markings for specific functions. Using your textbook as a guide, fill in this chart on the bone markings.


__Cleftlike opening

__Round opening

__Tubelike passage

__Airfilled cavity

__Depression for vessel or nerve

Fossa _


Condyle _

__Projection above a condyle

__Rounded projection on a thin neck

__Flat surface on ribs and vertebrae

Tubercle _

Tuberosity _

__Large, blunt process on femur

__Prominent border or ridge

Spine (spinous process) _

1. _ The sternum (breastbone) lies on the midsagittal plane of the body. Therefore this bone is part of the (axial/ appendicular) skeleton.

2. _ The carpals (bones of the wrist) have about the same length as width; therefore, they are (long/short irregular).

3. _ Bones which lie in the sutures of the skull are (3) bones.

7. _ Which kind of marrow is found in the central cavity?

8. _ Would you look in a diaphysis or an epiphysis to find cancellous tissue?

9. One student says that the cartilage at the end of a long bone is articular cartilage. Her fellow student says, "No, it is hyaline cartilage." Who is correct? Explain your answer.

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