MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 321 



ively the gyrus parietalis superior and inferior and represents the position of the 

 occipital lobe. 



At the point, PO, at which the external perpendicular becomes continuous 

 with the internal, but concealed within its depths, there develops in the monkeys, 

 from its floor, a small bridging convolution, 2, fig. 19, and the external perpen- 

 dicular fissure, 0\ is pushed backward just in proportion to the development of 

 this convolution ; the fissura interparietalis, i p, is also displaced to a corresponding- 

 extent downward and backward, and this is precisely the condition as found in 

 the human brain, with the exception that the fissu ration assumes a tortuous aspect. 

 In this manner the internal perpendicular appears as a fissure,. PO. nicking or ex- 

 tending slightly outward upon the lateral surface of the hemisphere. This is also 

 the case in the Orang according to Bischoff, and may be seen in the brain of Ateles, 

 Plate XXXVII, figs. 15 and 16, and also in the Chimpanzee on the right hemi- 

 sphere, Plate XXXVIII, fig. 13. This gyrus. 2, varies as to its extent of develop- 

 ment in different individuals. In all the negro brains that I have examined, I 

 found it much simpler than in the white. Below and back of this gyrus, 2, and 

 separated by the fissure surrounding it, we have evidently that part of the brain 

 which corresponds in Man to the smooth or progressively furrowed occipital region 

 of the Simiadge. Prof. Wilder, 1 remarks of Ecker's fissura occipitalis transversa, 

 as follows : " the reputation of Ecker, the clearness of his descriptions, and the 

 simplicity of his figures, with the existence of both English and American trans- 

 lations, have caused his statements and views to be accepted and his diagrams to 

 be generally reproduced, not merely in clinical reports, but in the papers of original 

 observers. But, although as I hope to show in a subsequent paper on the so-called 

 'ape fissure,' Ecker has clearly explained (pp. 5G-60, and note), some of the dis- 

 tinctions between the human and simian occipital lobe, yet his interpretation of the 

 morphological relations of the parts immediately surrounding the dorsal end of the 

 occipital fissure, which forms the natural starting point for the study of this region, 

 is not in accordance with what is indicated by the material examined by me, and 

 not even, as it seems to me, substantiated by his own descriptions and figures. In 

 Ecker's diagram of the dorsal aspect of the cerebrum (fig. 2), the right parietal 

 (interparietal) is made to stop nearly opposite the occipital, and there is a heavy 

 line extending across the base of the lobe, at little caudad of the occipital, and 

 wholly distinct from the parietal: this he calls the sulcus occipitalis transversus. 



" Ecker's interpretation of the relations of the parietal and transverse fissures 

 obviously depends upon the occasional independence of the latter, and I was led to 

 suppose that the small number of human brains accessible to me at the time of the 

 publication of Ecker's work might be more or less anomalous in the occipital 

 region. Recently, however, I have carefully examined all the brains in the 

 Museum of Cornell University, twenty-nine occipital lobes, and all the original 



1 "The Paroccipital, a newly recognized Fiesural Integer," Journal of Nervous and Mental Disease 

 (vol. xiii, No. 6, June, 1886). 



