On the Structure of the Brain in Man and Monkeys. 191 



evident. " I have found by a careful comparison of adult brains 

 ID men and monkeys, that they are arranged on the same plan as 

 to the g^'rations, and when the view is tlius limited to the adult 

 structure there is no marked ground for separating them. But 

 in studying the development 1 find that in apes the gyrations of 

 the posterior lobes appear before those of the anterior lobes 

 which is just the reverse of their succession in man. In one the 

 ^evelopement is from « to w, in the other from w to «, and hence 

 of a human brain can 



^v...i^i^ L.iciu v^i au upo. J.U10 v^viiclusion IS bomc out 



by a study of the brains of human microcephals. At first view 

 one of them might be taken for the brain of a new species of ape, 

 bat the least observation corrects the error. In apes the fissura 

 longitudinaUs* is always long and deep; in the human microce- 

 phal, this fissure is always incomplete and often wanting, the 

 sphenoid lobe being wholly smooth. Further, in the microce- 

 Phal, the second connecting gyration (le denxieme pli de passage) 

 between the occipital and parietal lobes which is a special char- 

 flf.fnv;„.:„ _^ ^j^^ surface. In the orang brain 



on me contrary it is constantly concealed under the operculum 

 of the posterior or occipital lobe. In its atrophied condition the 

 ^icrocephal brain, though it may be smaller and have fewer 

 gyrations than the brain of an orang or chimpanzee, still shows 

 |fs human character. The microcepbal or idiot however low is 

 ^0 animal, he is only a reduced human being. 



'■ 1 have endeavored to ascertain whether microcephalia pre- 

 cedes birth or not. In some microcephals the form of the brain 

 ^nd of the fissure of Sylvius showed the disease to be quite as 

 ^arly as the fifth month. Its cause is to be sought perhaps in 

 some general influence, some primitive genetic weakness (Astbe- 

 ^logenie) by which the abnormal form is produced. In the nor- 

 "^^ child at birth the gyrations of the brain are complete. This 

 ^s also the case with the young of all animals that are born with 

 open eyes, those that do not open their eyes till some time after 

 t"^-th do not complete the gyrations till then. If idiocy by ar- 

 fest of growth took place after birth the completed bram would 

 pontmue to show that completed structure, being infantine only 

 ^'^ size. Such is not the case however. The abnormal condition 

 occurs long before the curve of the brain is shortened and its 

 growth ends also earlv, before the normal period of close. The 

 enormous proportional development of the cerebellum in these 

 ;ttle beings is interesting, fof it is a proportion that puberty 

 J^ver attains. This fact is opposed to the theories of Gall m 

 J^gard to the functions of the cerebellum, but on the other hand 

 ^vors the views of Flourens. The microcephal usually moves 

 cj^^^We on the inner surface of the hembpherea just above the corpus 



