Anthropology P380: Lectures 11: Biomechanical principles for interpreting chewing capacity of hominids
The masseter muscle is one of several muscles that close the jaw during chewing. It originates at the angle of the mandible (jaw) and inserts on the front of the zygomatic arch (cheek bone).
The larger a muscle is, the more power it can exert. However, when evaluating the relative power of muscles, it is also useful to consider their leverage, using a simplified mechanical leverage system. Let’s use the masseter muscle as an example.
In a simplified lever system, the relative power of a muscle (its mechanical advantage) is determined by the ratio of leverage to load.
The load is what you want to move: in this case, the jaw! The "load arm" can be approximated as the distance from the joint to the front teeth.
The "lever arm" can be approximated as the distance from the joint along the load arm that the force is applied. The further away from the joint you apply your muscle force, the more leverage your muscle will have. The closer to the joint, the less effective or powerful the muscle will be.
As you look at different skulls in the lab, try to estimate the relative leverage of their masseter muscles. What features of skull architecture alter the leverage of the masseter muscle, either by decreasing the load arm or increasing the leverage arm?Class handout (pdf file)
Look at the two South African hominid skulls below. Which has a more powerful masseter muscle?
Australopithecus africanus
Paranthropus robustus
Syllabus | Readings | Lectures | Assignments | Discussion Forum
Human Origins and Evolution in Africa Home Page
Jeanne Sept's Personal Home Page
Last updated: 18 October, 1999
URL: http://www.indiana.edu/~origins/teach/P380syll.html
Comments: sept@indiana.edu
Copyright 1998 Jeanne Sept
