Sentence:  Briefly, the adoption of "calcar" is a logical corollary of the recommendation which is common to the reports of all four American committees, "vi.", "Other things being equal, it is recommended that <WSD>mononyms</WSD> be preferred to polynyms." "Calcar avis" is a polyonym ; "calcar" is a <WSD>mononym</WSD>. If it be said that "unguis" is also a <WSD>mononym</WSD>, the answer is that in this case "other things" would not be equal, because (1) no general preference has ever been shown for it or for any term of which it is a constituent; (2) there would be lost the advantage of the correlation now existing between the ental ridge and the fissure collacated therewith. 
Meaning of the word marked with <WSD> tags:  A single name by which a person, thing etc is known.