The “Pons Asinorum”

Wikipedia says:

Pons Asinorum (Latin for “Bridge of Asses”) is the name given to Euclid’s fifth proposition in Book 1 of his Elements of geometry, the theorem on isosceles triangles:

In isosceles triangles the angles at the base are equal, and, if the equal straight lines are produced further, then the angles under the base are also equal.

One hypothesis as to why the theorem is called the Pons Asinorum is that it separated the “intelligent” from the “fools,” who could not grasp the theorem. Answers.com says of the term Pons Asinorum:

The bridge of asses. Traditionally it is hard to get asses to cross a bridge. In mathematics, the term is applied to the problem from the first book of Euclid that if two sides of a triangle are equal then the angles opposite those sides are also equal. Syllogistic logic had its own pons asinorum: the inventio medii. The Oxford Dictionary of Philosophy. Copyright the Oxford University Press, 1994, 1996, 2005. Answers.com 13 May. 2009.

about which latter Answers.com says:

(Latin, the finding of the middle) In traditional logic, a name for a method invented by Petrus Tartaretus around 1480, by which the middle term of a syllogism can be found. It has sometimes been called the pons asinorum or bridge of asses of logic. The Oxford Dictionary of Philosophy. Copyright the Oxford University Press, 1994, 1996, 2005. Answers.com 13 May. 2009.

But the great historian of mathematics Sir Thomas Heath gave an alternative explanation of the meaning of the term (also from Wikipedia):

“But there is another view (as I have learnt lately) which is more complimentary to the ass. It is that, the figure of the proposition being like that of a trestle–bridge, with a ramp at each end which is more practicable the flatter the figure is drawn, the bridge is such that, while a horse could not surmount the ramp, an ass could; in other words, the term is meant to refer to the surefootedness of the ass rather than to any want of intelligence on his part.” (in “Excursis II,” volume 1 of Heath’s translation of The Thirteen Books of the Elements.)