OBJECTIVE: To present a background of terminology basic to the study of human osteology, and to acquaint the student with the histology and classification of bone.
Terminology
The following terms are used in anatomical and osteological description; it would be advisable for the student to become familiar with them at the onset.
The following terms describe anatomical directions and planes.
General
The skeletal system consists of the bony and cartilaginous framework of the body. The various skeletal components, the bones, structurally and functionally interact at the articulations, or joints as they are commonly called. Joints allow for body movement. The active force is supplied by the skeletal muscles, which are activated in turn by the nervous system.
The skeletal system – in addition to facilitating movement – supports the soft tissues (muscles, tendons, etc.) and thus is involved in body form. The skeleton is also protective, securely housing the brain and spinal cord within the skull and vertebral column, respectively. Also, the heart, lungs, and major blood vessels receive protection within the rib cage. Some of the bones are important centers of blood cell formation.
The skeleton gives stability to the body. When studied closely, each bone shows a structure based upon sound mechanics and engineering principles. The skeleton as a whole may however appear to be anything but stable, standing as it normally does on a small base (the feet) with a high center of gravity. Perhaps some stability may of necessity be sacrificed to gain versatility and freedom of movement. Furthermore, stability is a dynamic matter in a moving organism. The base can easily be broadened by moving the feet apart and the center of gravity lowered by flexing the foot, the knees, and the thighs. The trunk can be shifted to keep its line of gravity over the base. In sum, the human body has evolved a means to achieve the basic requirements of stability: a broad base, a low center of gravity, and a line of gravity which falls well within the base.
The number of bones in the skeleton varies at different ages. At birth, the human body contains about 270 bones. This number is slightly reduced during infancy by the union of some of the separate segments to form single bones, but from then on through puberty and adolescence the number increases steadily as the epiphyses and bones of wrists and ankles develop. After adolescence reduction is again brought about by a gradual union of independent bones. Ultimately the adult human skeleton consists of about 206 bones. They may be subdivided as follows:
Axial skeleton (80 bones): on the axis of
the body. The axial skeleton consists of:
Skull
29 bones
Vertebral
column 26
Thorax
Sternum
1
Ribs
24
(Costal cartilages)
Appendicular skeleton (126 bones): paired bones.
The appendicular skeleton includes:
Pectoral (shoulder)
girdle 4
Forelimb bones
60
Pelvic girdle
2
Hindlimb bones
60
Total:
206 bones
Classification of Bones by Shape
EXERCISES
1. On Figure 1, provide a label for each of the bones indicated by a line. Use this figure to assist in learning the names of bones of the skeletons in the laboratory.
2. Use Figure 1a to learn the planes of orientation.
3. Become familiar with the basic terminology listed in this exercise.
4. Complete the following sentences using the bones of your choice:
The _____________ is distal to the _________________.
The _____________ is posterior to the ______________.
The _____________ is superior to the ______________.
The _____________ is lateral to the ________________.
5. Please list the bones located at each of the two stations. Also, indicate which part of the skeleton they belong to (axial or appendicular) and their shape classes.
Station
1
Station
2
Figure 1. The skeletal system.
Figure 1a. The planes of orientation.