MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 319 



mesial occipitofrontal convolution above and the mesial occipitotemporal convolution 

 below. The arrangement as found'm this low American monkey represents on the 

 mesial surface the morphological type on which all the Simian and human brains are 

 based. The differences that are observed in the higher monkeys and in Man are due 

 merely to secondary complications, and it will be found that these secondary modifi- 

 cations conform to definite and regular laws. The portion of the fissure, o\ seen on 

 this surface, PI. XXXVIII, fig. 8, represents the internal perpendicular or parieto- 

 occipital of Man. With regard to this point, an immense amount of confusion 

 exists, Gratiolet, Marshall and others being entirely wrong in their identifications in 

 the human brain. Thus Marshall, following Gratiolet, in describing the brain of a 

 Bushwoman, calls the lateral portion of the parietooccipital the external perpendicu- 

 lar fissure, identifying it with the external perpendicular of the apes. This identifi- 

 cation is incorrect and has been one of the most fruitful causes in producing much 

 of the confusion as regards the fissures and convolutions of the occipital lobe. Pansch 

 and' Ecker recognize the true condition, but do not properly apply it ; thus, Pansch 

 in speaking of the fissura occipitalis externa, remarks, " I have very seldom found an 

 indication of this fissure in the foetal brain, and I cannot find in the adult brain any 

 indication in this region of a typical furrow. 1 mean that had the human brain been 

 examined alone (I speak only as regards foetal brains now before me) one could not 

 arrive at the conclusion that the fissura occipitalis externa is a fissure of importance 

 equal to the others, or as at all to be regarded as a typical furrow. Of course it is 

 true that we see here frequently a transverse fissure, but either it is very shallow or 

 it varies very much in different brains and is very short. That Ave find in many 

 brains a fissure which corresponds to the so-called fissura occipitalis of the apes 1 do 

 not deny, but only that it is a typical furrow of the human brain." 



Bischoff rightly identifies the internal perpendicular, but he introduces fresh con- 

 fusion. In the foetus he identifies the external perpendicular, but he states that it 

 disappears in the seventh and eighth month on account of the development of new 

 fissures and convolutions in this region. He says that he is not in a position to 

 maintain that a furrow appearing on the outer side and a nick often found on the edge 

 between the inner and outer surface is not a remnant or further development of this 

 fissure. It corresponds distinctly, however, with the occipital fissure found in the 

 majority of the Simiadae and which separates the parietal and occipital lobes. On 

 this subject Ecker expresses the following opinion with which I entirely concur : 

 " Bischoff mentions the fissura perpendicularis externa which arises at the end of the 

 seventh month and descends perpendicularly over the posterior part of the hemis- 

 phere, but is not further developed and does not give origin to any permanent fur- 

 rows, but in the eighth month entirely disappears without taking part in the forma- 

 tion of the furrows later noticeable in the occipital lobe. Of course it is very easily 

 possible that a furrow which exists for such a short time, so that it has a life of only 

 three weeks, can very easily escape the notice of an observer, and I am very far 

 removed from wishing to throw doubt on this observation of Bischoff*. That the fur- 

 row, however, which I designate as fissura occipitalis transversus, and which is fre- 



40 JOURN. A. X. S. PHILA., VOL. X. 



