MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 341 



2. The mesial arched fissure. J L Fissura callosalis. 



i 2. " hippocampi. 



3. The fissura calcarina. 



These fissures are closely related to the three lobes of the brain. The Sylvian 

 divides the hemisphere anteriorly into the occi pi to-frontal and occipito-temporal 

 lobes; whilst the remaining three found on the mesial surface (and constituting 

 the fissura triradiata of the writer) are symmetrically related to the three horns of 

 the lateral ventricle, which in its turn forms a tri radiate cavity corresponding to 

 the three lobes of the tri-radiately developed hemisphere. 



The secondary fissures include in their fully developed state three occipito- 

 frontal fissures and three occipito-temporal. Of these two are lateral and one 

 mesial, in both the occipitofrontal and occipito-temporal lobes, and mark out in 

 each a mesial occipi to-frontal or temporal and three lateral occipito-temporal or 

 frontal convolutions. Separating these from and marking off the boundaries of the 

 occipital lobe we have the primary occipital arch. O 1 , 2 . 



These fissures include all the fissures that I would include in this second 

 group, but some of these divide as we have already seen into two or more impor- 

 tant fissures which have received distinct and separate names. Figs. 5 and 6, 

 Plate XLIII. gives the ideal type of arrangement ; figs. 7 and 8. as found in Man ; 

 figs. 9 and 10, in the Chimpanzee ; and figs. 3 and 4, Plate XLIV, in the brain 

 of the human foetus toward the close of the ninth month. 



The names of these fissures and convolutions, with those of their component 

 parts when they become separated, are as follows : 



I. OCCIPITO-TEMPORAL LOBE. 



1. Superior or first occipito-temporal fissure, o. t. 1 



2. Middle or second " " " o. t. 2 



3. Mesial " " " m. o. t. 



These form separate occipito-temporal convolutions which preserve the same 

 relations when completely developed, throughout all the Primates. 



1. Superior or first occipito-temporal convolution. 0. T. 1 . 



2. Middle or second " u " 0. T. 2 . 



3. Infer ior or third " " " 0. T.". 



4. Mesial occipito-temporal or gyrus hippocampus M. 0. T.. 



II. OCCIPITOFRONTAL LOBE. 



1. Superior or first occipi to-frontal fissure, o. f. 1= = Superior frontal V + fis- 



sura centralis c. 



2. Middle or second occipitofrontal fissure, o. t\-=Middle frontal f. 2 + the 



interparietal fissure i. p. 

 -3. Mesial occipitofrontal fissure, m. o. K = Callo so-marginal fissure. 



