by Matthew Law

The humerus is the uppermost bone of the arm. It is comprised of the shaft and epiphyses, which fuse in adolescence

It is said to have 2 'necks' - the anatomical neck and the surgical neck

ANTERIOR

There is a groove in the front of the humerus (best seen from the top) called the mycipital groove. A tendon for the biceps runs through here. Sometimes there is a faint marking for the transverse ligament, which stops the biceps bowing.

The flat area on the head of the humerus is where the four muscles of the rotator cuff meet. These are

1. subscapularis
2. supraspinatis
3. infraspinatis
4. teres minor

There is often a lot of pathology in individuals aged 40+ in this area.

The roughened area halfway down the shaft is for insertion of the deltoid muscle.
Vigourously used muscles have larger insertions.

At the bottom, there are two joints. The bigger is the trochlea, and the smaller, which is round, is the capitulum, which is for the head of the radius.
There are two protrubences - medial and lateral epicondyles. The medial epicondyle is for the ulnal nerve (which gives the 'funny bone' sensation).

The coronoid fossa is a small depression above the trochlea.
The radial fossa (often indistinct) is a small depression above the front of the capitulum

POSTERIOR

There are insertions for infraspinatus and teres minor.
There is a very large depression at the bottom - the olecranon fossa. Archaeologically, this is often broken.

There are lots of holes around the head of the humerus, these are entry points for blood vessels. There are more around the end of bones than the shaft because the ends are more metabolically active.

MEASUREMENTS
In the laboratory, a few routine measurements are taken of the humerus - these should be recorded to the nearest millimetre
1. Maximum length
2. Maximum diameter of the head

The diameter distinguishes sexes. Greater than 45mm is usually male.
Length could be used to estimate height.

NON-METRIC VARIABLES

Either these are there, or they aren't! There is no gradation.

e.g. Septal aperture - in the bottom of the humerus, has nice smooth round edges.

Supracondylar process - a hook near the bottom - this is an atavistic feature, found in carnivores. There is a very low prevalence of people having this. c. 1 in 1000. Sometimes the median nerve gets trapped in there.

FURTHER READING

White, T.D., and Folkens, P.A., 2005, The Human Bone Manual (San Diego: Academic Press) Chapter 12 is on the arms.

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