MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 317 



CONVOLUTIONS AND FISSURES OF THE OCCIPITAL LOBE. 



We now come to the consideration of the fissures and convolutions of the occi- 

 pital lobe, and here we approach, as we have before remarked, perhaps the most con- 

 fused subject in the Avhole range of anatomy. Ecker, in speaking of this lobe, 

 remarks that there is indeed no doubt that the understanding of the convolutions of 

 the occipital lobe is more difficult than that of all the other lobes. He regards this 

 difficulty as arising from the great individual variation, and by the transference of 

 the nomenclature of the monkejr brain directly to that of Man. He says that in no 

 part of the cerebral surface is the difference between the brains of the apes, Cerco- 

 pithecus, Indris, Cynocephalns* Cebtis, etc., upon which Gratiolet's description was 

 founded, and the human brain, more marked than in the occipital lobe. He con- 

 siders that the various connecting convolutions, the plis de passage of Gratiolet, may 

 have a meaning in the lower apes, but none at all in Man. He says, " the separation 

 of certain intermediate portions under the name of transition convolutions, plis de 

 passage, between the convolutions of the occipital lobe on the one hand and the 

 parietal and temporal on the other, has no justification in the human brain, and 

 makes this understanding of the region more difficult. I have, therefore, wholly 

 rejected the name." I cannot wholly agree with Ecker as regards these transition 

 convolutions in the human twain, and, farther on, I will endeavor to point out what 

 appears to me to be their exact significance. The attempt to separate these parts as 

 distinct convolutions in the human brain, as has been done by Gratiolet and the 

 English anatomists, is certainly productive of confusion, and gives an erroneous 

 interpretation to this region. Indeed, even in the monkeys, I do not think they 

 should be considered as separate convolutions in any sense comparable to the other 

 gyri of the cerebral surface. I cannot, however, agree with Ecker in the statement 

 that the confusion arises from the transference of the nomenclature of the monkey's 

 brain to that of Man. It is true, confusion has arisen, but it appears to me that this 

 is owing to the faulty method of considering this lobe and not to any essential differ- 

 ences existing in the arrangement of the lobe in Man and the Simians. I believe if 

 these lobes be rightly compared, not only can the nomenclature of the ape brain be 

 transferred directly to that of Man, but positive advantage arises therefrom, and 

 many points that appear unimportant and obscure in the human brain assume new 

 and interesting relations, and acquire a deep significance when viewed from a morpho- 

 logical standpoint. Complex nomenclature and the identification of secondary 

 fissures as of primary importance, together with the non-recognition of the true 

 relations existing between the convolutions and fissures of this lobe, appear to me to 

 be the causes of this confusion. Before describing the occipital lobe as it exists in 

 Man, it will be necessary, on account of its more simple character, to study its struc- 

 ture and mode of arrangement in the Simidae. We have already pointed out in dis- 

 cussing the boundaries of this lobe in these animals that it can be almost completely 

 separated from the occipito-frontal and occipitotemporal portions by two transversely- 

 running fissures, o 1 and o 2 forming together what I have termed the primary occipital 



