The origin of the Cuneiform Syllabary.--As we have seen, the pictorial origin of the cuneiform characters was perceived in the early days of Assyrian decipherment, as well as the cause of their polyphony. Their wedge-like forms were due to the use of clay as a writing material. The impression made by the stylus upon it resembled a wedge; curved lines became angles, and after a time the original picture passed into a conventional form. In the course of centuries the characters grew more and more simplified by the omission of unnecessary wedges, the least complicated being those of the official hand of Assyria, and the later Babylonian or Persepolitan script. It must not be supposed, however, that when the system of writing ceased to be pictorial it was already complete. Down to a comparatively late period new characters were invented or old characters combined in a new way, while new phonetic and ideographic values were assigned to the characters which already existed. Though the syllabary is essentially of Sumerian origin there is much in it which is traceable to a Semitic source. Many of the values given to the characters as well as many of their ideographic meanings are Semitic. Moreover the Sumerians and Semites lived in contact with one another long after the adoption of Sumerian culture by the Semitic nomads; consequently not only did the Semites borrow Sumerian words, the Sumerians borrowed Semitic words, more especially in the northern part of the country. The early date at which some of these were borrowed is shown by their having undergone the phonetic changes which distinguished the northern Accado-Sumerian dialect from the southern. False etymologizing also has given rise to new values just as it has given rise to new spellings in English. The Semitic scribes of a later day were as fond of deriving Semitic words from Sumerian as our own etymologists used to be of deriving Teutonic words from Latin, Greek, or Hebrew. Thus the purely Semitic _sabattu_ 'Sabbath,' from _sabâtu_ 'to rest,' is derived from the two Sumerian words _sa_ 'heart' and _bat_ 'to complete,' and interpreted to mean 'a day of rest for the heart.'