19.2.5 Ordinals.

Ordinal numbers generally express order or rank, rather than a precise quantity. Because they usually address nontechnical aspects of the objects they modify, ordinals are often found in literary writing. The numerical expression of commonly used ordinals (1st, 2nd, 3rd, 4th, etc) may appear jarring and interrupt the flow of the text. For this reason the ordinals first through ninth are spelled out.The third patient was not available for reevaluation. It has become second nature.The numeric form of ordinals greater than ninth is well established in literary texts (10th, 11th, and so on) except at the beginning of a sentence, ...Less