But there was probably an advance made which we do not find recorded, or only equivocally recorded, in the memorials of the age. Speech was probably the greatest invention of Magdalenian man. It has been pointed out that the spine in the lower jaw, to which the tongue-muscle is attached, is so poorly developed in Palaeolithic man that we may infer from it the absence of articulate speech. The deduction has been criticised, but a comparison of the Palaeolithic jaw with that of the ape on one hand and modern man on the other gives weight to it. Whatever may have been earlier man's power of expression, the closer social life of the Magdalenian period would lead to a great development of it. Some writers go so far as to suggest that certain obscure marks painted on pebbles or drawn on the cavern-walls by men at the close of the Palaeolithic Age may represent a beginning of written language, or numbers, or conventional signs. The interpretation of these is obscure and doubtful. It is not until ages afterwards that we find the first clear traces of written language, and then they take the form of pictographs (like the Egyptian hieroglyphics or the earliest Chinese characters). We cannot doubt, however, that articulate speech would be rapidly evolved in the social life of the later Magdalenian period, and the importance of this acquisition can hardly be exaggerated. Imagine even a modern community without the device of articulate language. A very large proportion of the community, who are now maintained at a certain level by the thought of others, communicated to them by speech, would sink below the civilised standard, and the transmission and improvement of ideas would be paralysed. It would not be paradoxical to regard the social life and developing speech of Magdalenian man as the chief cause of the rapid advance toward civilisation which will follow in the next period.