General Considerations

The lower extremity is designed to bear the weight of the body and serve as a means of locomotion.

It is composed of a pelvic girdle, thigh, leg, and foot.

The pelvic girdle serves as the medium of connection of the lower extremity to the trunk in the same manner as does the shoulder-girdle for the upper extremity.

We saw that prehension, characterized by mobility, was the distinguishing feature of the upper extremity and that the shoulder-girdle was composed of two bones, was loosely joined to the trunk, and held the upper extremity out away from it.

The lower extremity on the contrary has two functions, it must bear the weight of the body and must move this weight around from place to place; hence strength is essential and a less amount of mobility suffices. To meet these changed conditions the lower extremity differs in its construction from the upper in the following respects:

1. The pelvic girdle is composed of one bone - the innominate - instead of two.

2. It also forms a part of a complete bony ring instead of being incomplete posteriorly.

3. It is more firmly joined to the trunk.

4. The hip-joint is placed closer to and in more intimate relation with the trunk than is the shoulder.

5. The bones of the lower extremity are heavier and stronger than those of the upper.

6. The joints are larger and stronger, but their movements are not so extensive.

7. The muscles are coarser and their functions are not so highly specialized.