The right ear of Garamond’s M – almost as famous and mysterious as Van Gogh’s left ear.

The short version is that Jenson’s M had bracketed top serifs extending outward and inward.
See (a) in the illustration below.

The M of Aldus Manutius’ typeface had only one ear on the left and no right-hand top serif
See (b) in the illustration below.

Early Garamond typefaces followed this 'one-eared' approach, and it was only later that these typefaces got two top serifs extending outward.
See (c) in the illustration below.

Fot this reason it was assumed that Garamond copied Aldus’ typeface.
This theory is quite convincing.

The only problem that there were four or five punchcutters around at the same time (including Augereau, Gryphius, de Colines, Garamond and some others) who were designing typefaces of a similar, new style (what is nowadays called ‘Garamond’), and it is very likely that some of the typefaces which were formerly attributed to Garamond were actually designed by someone else.

This article has more information:
Hendrik D. L.Vervliet: ‘The young Garamont: roman types made from 1530 to 1540’, in: Typography Papers no 7 (2007), pp 5–60

[The illustration is from Vervliet’s article: ‘The young Garamond’. It shows the principle of the top serifs, not the real, original typefaces]

For more info about Garamond see also: Typowiki –> typefaces –> Garamond
http://typophile.com/node/12481?

it seems that uploading the picture didn't work – sorry. Have a look at Vervliet's article and you will find plenty of Ms

Thanks a ton for the article, I'll go take a look!

courtney