282 



MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 



prolongation of two fissures, one in the frontal and the other in the occipital lobe, 

 fissure 4 running parallel to and with the same inclination as the axis of the Sylvian 

 fissure. 



In the occipitotemporal lobe we find three furrows radiating from a centre 

 common with those of the occipitofrontal and following the direction of the pro- 

 longations of the axes A Y and 2, 7. 



The posterior prolongation of the hemisphere forming the occipital lobe seems 

 to be symmetrically developed in a relation to a centre of its own, which is situ- 

 ated at the junction of the three horns of the lateral ventricle at B. fig. 2, and 

 Plate XXXV, fig. 4. Two fissures, 5 and 6, separate the occipital region, 0, from 

 the occipito-frontal above and the occipitotemporal below, and are prolonged out- 

 ward for some distance upon the lateral surface' of the hemisphere. On the mesial 

 surface they are inclined at an angle of 60° to B, X, and are, therefore, respectively 

 parallel to the axes of prolongation 2, 7, and A 4. These two fissures cut off a 

 posterior rhomboidal shaped mass, which, more or less modified, becomes the future 

 occipital lobe. 



Besides the radiating fissures we also find upon the mesial surface an arched 

 fissure surrounding the corpus callosum and fornix, the Bogenfurche of Arnold, 

 or, as I should prefer to call it, the mesial arched fissure (fissura arcuatus medialis ) 

 This fissure remains as a permanent fissure, described, however, as two separate 

 fissures, the callosal, surrounding the corpus callosum and following the anterior 

 horn of the lateral ventricle, and the hippo-campal, following the course of the 

 descending horn. Indeed, these two fissures, or as a whole the mesial arched fis- 

 sure, depend for their formation upon the presence of these two cavities, and it can 

 readil} r be seen that the same forces which urge the two hemispherical sacs into 

 contact in the median plane, would also, if continued, produce this crescentic inroll- 

 ing into the ventricles, forming an arched fissure following in this way the course 

 of the corpus collosum and fornix. 



In the same manner there is produced, as a resolution of the pressure forces, 

 an inrolling into the posterior horn of the lateral ventricle, the fissure B X, fig. 2, 

 which is also a permanent fissure and becomes the future fissura calcarina. Thus 

 Ave find at this early stage the permanent fissures of the mesial surface have 



a tri-radiate arrangement corresponding 

 with that of the lateral ventricles. The 

 accompanying diagram, fig. 3, will render 

 plain the morphological type of fissuration 

 as regards the permanent fissures of the 

 brain at this early stage in its development. 

 For the fissure as a whole I propose the 

 name fissura tri-racliatus or fissure of the 

 ventricle. For the arched portion (Bogen- 

 furche) the name fissura arcuatus medialis, 

 consisting of an upper anterior portion, the 



Fig. 3. 



Tr : F. tri-rad. ma : mesial arched. 

 CI. Callosal : Hp. Hippocampal. 

 Ca : Calearine. 



