MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 337 



displacing in their turn the operculum, and pushing it backward. On reaching the 

 surface they then appear in their true light as posterior portions of the convolutions 

 situated anteriorly. 



We have already expressed the opinion that of all the morphological theo- 

 ries which thus far have been advanced to explain the convolutional configura- 

 tion of the human brain. Huschke's approaches most nearly the truth. Through 

 his studies in embryology and comparative anatoim- he believed that in the brain 

 there are three or four ground convolutions which arch in the form of a horse- 

 shoe backward around the upper horizontal branch of the fissure of Sylvius and 

 extend downward into the temporal lobe to the borders of the same. While 

 these ground convolutions are more or less recognizable in the brains of the lower 

 orders of mammals, in Man and the ape they are split by the development of 

 the fissure of Rolando or central fissure and its accompanying convolutions, the 

 relations being as follows: In the middle of the hemisphere we have the central 

 fissure with its accompanying convolutions. In front of these there are three fron- 

 tals, running longitudinally: the first, second and third; back of these are like- 

 wise three wiiich run backward and toward the end of the hemisphere but only the 

 upper two reach the same, the lower running around the Sylvian fissure and 

 extending into the temporal lobe, which is also formed by the upper and middle 

 convolutions after they have reached the back end of the hemisphere proceed- 

 ing forward. These posterior convolutions coil themselves more than the frontal 

 and form, therefore, lobules; and in truth three upper lobules; the lobulus parie- 

 talis superior or Vorzwickel, the cuneus or Zwickel and a third the end lobule 

 (medio-posterior occipital of writers). The middle and lower convolutions which 

 are considered as one. also show three lobules. Whilst the non-recognition of 

 a distinct occipital lobe rendered this view of Huschke's faulty and imperfect. 

 it still coutained, I believe, germs of a true theory and correlates, in a gen- 

 eral way. the convolutions of the Primate brain with those of other existing 

 orders of mammalia, especially the carnivora. The arrangement as found in the 

 fox, etc., is shown in PI. XLV, figs. 1 and 2, etc.. indicating that the type of fis- 

 suration in these animals consists of three or four primitive lateral arching con- 

 volutions separated from each other by a fissure corresponding to the Sylvian 

 and two arching fissures similar to three more or less confluent occipito-frontals 

 and occipito-temporals. A comparison with the brain of Cheiromys. PI. XXXIV, 

 fig. 24, will show some decided resemblances. Evidently the structure of the 

 occipitotemporal and the frontal portion of the occipito-frontal in Man and the 

 Simiadee is due to similar growth conditions, and if we add to the carnivorous 

 type of brain a distinct occipital lobe, meeting and cutting off the posterior con- 

 nections of the two upper lateral occipito-frontals from the two lower lateral 

 occipitotemporal convolutions, we shall have the type, which more or less imper- 

 fect and modified we find in the Lemurida? ; and which is still retained and fur- 

 ther modified in the Simiada? by the separation and formation of the fissura cen- 

 tralis in a manner previously described. 



