Sentence:  Thus, when he drew up instructions in lawyer language, he expressed the important words by an <WSD>initial</WSD>, a medial, or a final consonant, and made scratches for all the words between; his clerks, however, understood him very well. 
Meaning of the word marked with <WSD> tags:  Spatially first, placed at the beginning, in the first position; especially said of the first letter of a word.