cheeky protuberances

Jack Windsor Lewis in his blog 408 describes the results of his consultations of various dictionaries with regard to the pronunciation(s) of the adjective callipygous. Had I been pressed to pronounce this word when I first came across this item hitherto unknown to me, I would have said: /kæˈlɪpɪgəs/. But most of the dictionaries place the main stress not on the antepenultimate but on the penultimate syllable.

credit: source unknown

Why so? A disclaimer first. "I am neither a Greek nor a Latin scholar. All statements, conjectures and hypotheses as to the stress assignment in Greek and Latin nouns and adjectives are likely to be erroneous and at best provisional."
After this exculpation here's my personal and private explanation:
According to the OED the adjective goes back to Greek καλλίπῡγος. The second constituent has a long < ῡ >. A long vowel means a heavy syllable, and a heavy syllable receives the stress in Latin. The consequence for callipygous is that the penultimate syllable should receive the main stress.This is what usually happened to such Greek polysyllabics that entered the English language via Latin.

On the other hand there's the beautiful writer, the calligrapher. The Greek καλλιγράϕος has a light penultimate syllable (no long vowel, no syllable-final consonant cluster), so the main stress falls on the penultimate in the Latin equivalent, which results in the English pronunciation /kəˈlɪɡrəfə/.
... I humbly await the wrath of the expert on Greek/Latin ...

My thanks go to J Windsor Lewis for drawing my attention to the word callithumpian, which according to the OED is a US colloquial term (adjective or noun) referring to a band of discordant instruments or to one of its band members. The stressing of the latter formation should be much less doubtful.

J Windsor Lewis mentions platypygous (with two y's in the OED) and steatopygous and adds the comment:

"We sadly seem t've [sic] allowed the attractive word platypigous for 'broad-bottomed' to lapse into obsoletion." 

True as this is in regard to the word as such, the concept, however, has definitely not fallen into oblivion - at least not for me.

Finally, I should like to make mention of Thomas Brown's Pseudodaxia Epidemica of 1646 (I checked the 4th ed. of 1658). Here we find this quotation:

 "If so, then men with great bellies will float downward, and onely Callipygæ, and women largely composed behind, upward." (p. 247) 

I'm not going to dwell upon the yucky details of this chapter.

Sir Thomas Brown (1605-1682)