396 SCIENCE PROGRESS 



if the form of this process reflects so intimately the form, and 

 mass, of the temporalis muscle that he can tell from its inspec- 

 tion in the Piltdown jaw what was the precise character of 

 the temporalis inserted thereon, then the coronoid process of 

 male chimpanzees' jaws in which the temporalis extended to 

 the middle line of the skull should be readily distinguished from 

 jaws in which this muscle failed to reach the median line, as 

 in some males, and most female chimpanzee jaws. Yet such 

 discrimination is impossible. On the contrary, the precise 

 factors which mould the form of the coronoid process and 

 of the sigmoid notch so far defy discovery, if only because of 

 the extreme variety which they present. Typically, in the 

 chimpanzee, the sigmoid notch, on which the form of the 

 coronoid process largely depends, runs directly downwards and 

 forwards, in a straight line from the condyle to the very base 

 of the process in question, which commonly ends in a hook- 

 shaped and backwardly directed summit. In some individuals, 

 however, this notch is excessive^ deep and narrow, when the 

 coronoid process closely approaches the condyle, as a glance 

 at the accompanying figures will show. A notch of this latter 

 type seems always to be associated with a very small jugal 

 fossa. But save for this apparent correlation between the 

 form of the jugal fossa and the ascending ramus of the man- 

 dible, no other governing factors in these extremely variable 

 features seem discoverable. The dissimilarities of the ascending 

 ramus of the mandible of the chimpanzee is remarkable, having 

 regard to the restricted area of distribution of this animal. 

 To find its parallel among human jaws all the races of the 

 world must be sampled. 



Great stress is laid on the significance and importance of 

 the " secondary ridgelets " associated with the " ridge which 

 extends upwards from the base of the coronoid process which 

 gives extreme strength of attachment to the muscle fibre. 

 This stage of roughening on the mandible is associated in the 

 chimpanzee with the closest approach of the upper end of the 

 muscle to the median line of the brain-case and especially with 

 the formation of a sagittal crest. It is well marked in the 

 Piltdown jaw." These very circumstantial statements have 

 no support in fact, at any rate in any of the specimens I have 

 examined. The " ridgelets " are nowhere very obvious, and 

 are no better developed in male than in female jaws, and 



