DR DUBOIS ON PITHECANTHROPUS ERECTUS. 83 



sulcus and having the shape of a reversed cc . The two segments 

 of this figure encircle the two limbs of perfectly definite Y-shaped 

 anterior branches of the fissura Sylvii, the stem of which is about 

 I cm. long. 



The second frontal sulcus is only very partially preserved on the 

 left side. 



On both sides a medial frontal fissure is very marked. 



The first frontal fissure is interrupted in different pieces, a con- 

 dition common in the apes as well as in man. 



The important inferior frontal convolution has attained a fair 

 development. I found the area of its exposed superficies equal to 

 half the average area in twelve European hemispheres, but at least 

 double that in the brain of a large chimpanzee or an orang-utan. 

 This seems to indicate that our fossil being possessed already a 

 certain amount of power of speech. The pars triangularis is 

 present in this convolution, as results from the presence of two 

 anterior branches of the Sylvian fissure. But the pars opercularis 

 has only a very rudimental development. This part in man Broca 

 regarded as the motor centre of speech, but later researches, 

 especially by Beevor and Horsley on apes, and pathological obser- 

 vations have shown that the region in the cerebral cortex which 

 presides the movements of the phonation-muscles is somewhat 

 more extensive. By some pathologists even the whole inferior 

 frontal convolution is brought in connection with phonation. More- 

 over in the brain of men who were not dumb at all the pars oper- 

 cularis very commonly is found but poorly developed. 



In the opinion of Cunningham and ^larchand the sulcus rectus 

 of the apes is the homologue of the sulcus frontalis inferior of man, 

 from which it would follow that the inferior frontal convolution in 

 the apes should be relatively of much larger extent than that of man, 

 certainly a very improbable assumption. Herve, Eberstaller, Wal- 

 deyer and others however regard the sulcus rectus of the apes as 

 homologous with the sulcus frontalis medius of Eberstaller in man, 

 and as the real homologue of the inferior frontal fissure (including 

 the annexed sulcus fronto-marginalis) of man they regard the 

 sulcus fronto-orbitalis of the apes. 



The opinion of the latter anatomists is fully dealt with by the 

 much regretted Italian anatomist Giacomini. Having examined a 

 larger number and a more complete series of microcephalic brains 

 than any other observer he could clearly follow the gradual transi- 

 tion from the most ape-like fronto-orbital sulcus to the perfectly 

 human inferior frontal sulcus and did not hesitate in adopting 

 similar views. 



I can the easier abstain from a longer trespass on the contro- 

 versial ground of the homologies of the frontal sulci and con- 

 volutions since we have here in the person of Professor Waldeyer 

 one who is fully entitled to give his opinion in the matter. Only 

 I wish to draw your attention to the fact that however in this fossil 



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