C. The appearance of the higher type of humanity in the period next following the Mousterian, viz. that distinguished by the Aurignacian type of implement, has now to be discussed. As already remarked, the man of Aurignac, as compared with him of the Neanderthal, has less protruding jaws, the lower jaw in particular being provided with the rudiment of a chin, while the limb bones are slender and altogether of the modern type. Upon such contrasts a remarkable theory has been based by Professor Klaatsch[49]. He made a comparison between the anthropoid apes on the one hand, and the two human types on the other (Fig. 28). As a result, he pointed out that the Orang-utan differs from the Gorilla much as the Aurignac does from the Neanderthal man. Assuming this statement to be correct, a hypothesis is elaborated to the effect that two lines of human descent are here in evidence. Of these one includes an ancestor common to the Orang-utan (an Asiatic anthropoid ape) and the Aurignac man; the other is supposed to contain an ancestor common to the Gorilla (of African habitat), and the Neanderthal man. [Illustration: Fig. 28. Various thigh-bones arranged to shew the alleged similarity between _A_ Orang-utan and _B_ Aurignac man, as also between _C_ Neanderthal and _D_ Gorilla. _A_ and _B_, while resembling each other, are to be contrasted with _C_ and _D_. They are referred to as the A/O and N/G groups. (From Klaatsch.)] The further development of the story includes the following propositions. The more primitive and Gorilla-like Neanderthal type is introduced into Europe as an invader from Africa. Then (at a subsequent epoch probably) an Asiatic invasion followed. The new-comers owning descent from an Orang-utan-like forerunner are represented by the Aurignac skeleton and its congeners. In various respects they represented a higher type not only in conformation but in other directions. Having mingled with the Neanderthal tribes, whether by way of conquest or pacific penetration, a hybrid type resulted. Such was the origin of the Cro-magnon race. The hypothesis has been severely handled, by none more trenchantly than by Professor Keith[50]. A notable weakness is exposed in the attribution to the ancestors of the Orang-utan so close an association to any human ancestral forms, as Professor Klaatsch demands. To those familiar with the general anatomy of the Orang-utan (_i.e._ the anatomy of parts other than the skeleton) the difficulties are very apparent.