He knew that a vowel may be omitted; and it is certainly strange that he never suspected that the two intervening letters might express ‘muz,’ and the whole give him ‘Aurmuzda.’ In deference to the Murgab inscription he had already changed his original _z_ into a _k_, and his _sch_ into _sr_; and we should think he might have seen sufficient ground in what has been said to justify his abandoning the _o_ _gh_. His singular attachment to _o_ _gh_ prevented him from observing that the fourth letter in this word is the same as the letter that follows ‘aka’ in the other; and it is curious he did not see that an _m_ in one case would help him on with ‘Ormuzd,’ just as an _m_ in the other would lead up to ‘Akam[enian].’ There was an additional reason indeed for his changing his _o_ into _m_, for he knew that (according to Anquetil) _m_ was the sign of the accusative—a form from which he was forced to depart when he made _o_ an accusative termination.[324] If he had advanced to ‘akam,’ we can scarcely suppose that he would have failed to recognise ‘Achaemenian,’ and would have modified his transliteration in accordance with this new discovery. It was the identification of _m_ and _n_ long afterwards by Rask that to a great extent facilitated the way for farther progress towards completing the alphabet, an opportunity that Grotefend unfortunately allowed to escape him. One of the chief services rendered by Grotefend to the alphabet was to draw up a long list of the various signs he found in the inscriptions which were evidently due to errors on the part of the copyist. These he ascertained by a careful collation of the inscriptions as they appeared in the works of Le Bruyn, Niebuhr, and others.[325] Even Niebuhr had admitted eight of these into his corrected list of forty-two letters, but they existed in great numbers in the inscriptions, and till cleared out of the way, they presented a serious obstacle to the decipherer. Some of his detractors, like St. Martin, have accused him of wilfully excluding these signs, or of changing them arbitrarily to suit the exigencies of his own system; but the charge is entirely without foundation, as De Sacy recognised from the first.