7^ SCIENCE PROGRESS 



can be found of the separate constituents, which should have 

 presumably remained as vestiges of the reptilian type. 

 " Meckel's cartilage atrophies in its greater part, but its front 

 part, taken into the bone, is ossified, and probably therefore 

 represented in the bone between the mental foramen and the 

 symphysis, and is possibly responsible for the prominence of 

 the chin." * The lower jaw is also instructive, as from it a 

 far-reaching principle may be deduced in regard to the late 

 evolution of the bones. The Heidelberg and other very early 

 human jaws are large, thick, and clumsy. In particular the 

 sigmoid notch is nearly absent. But it is not probable that 

 the presence of this notch and of a light " elegant " bone would 

 of itself be a character of survival-value. We here probably 

 meet some force which is present in most surviving mammals, 

 but which was not so marked in extinct ones. This force 

 makes for economy in the substance of the bone, with the 

 distribution of the material in such a way that the maximum 

 of strength is attained in any required direction. We shall 

 see that in the case of man economy in bony structures has 

 been correlated with the special growth of the brain. Absence 

 of present-day markings on the jaw for the attachment of 

 muscles may be a character of doubtful value, as an indication 

 of the absence of the power of speech. 



A similar story is unfolded in the embryological history of 

 the tail in man and the apes. The scaffolding for at least six 

 separate bones is faithfully laid down in cartilage, such being 

 apparently the length of the tail in the primitive ancestor. 

 The outline of the first four is seen in the coccyx, but the last 

 two are so small that they disappear by being absorbed into 

 the fourth segment. On the current theory of vestiges it would 

 appear that, as the premaxilla has disappeared more completely 

 than the tail, it was the earlier of these two structures to be 

 lost by the human stock. 



2. The foot has always been recognised as a special feature 

 which played an essential part in establishing the mental 

 superiority of man. The older anatomists looked upon the 

 upright gait as the indication of a gap sufficient to justify the 

 definition of a special Order, Bimana, for man alone. But 

 since the death of Owen man has been grudged even a Family 

 for himself. Current opinion is thus stated by Pocock : " The 

 moment we get to the apes we see a progressive series of 

 modifications, beginning with the gibbon, ending with the 

 chimpanzee or gorilla, attesting most clearly the stages of the 

 evolution of the human foot from the ape type." ^ Here the 

 genetic relationship is inferred, and the progressive series is 



* Frazer, Anatomy of the Human Skeleton, 1914, p. 250. 

 2 Pocock, in Conquest, February 1920. 



