342 MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 



These separate, according to the view held in this paper, a number of distinct 

 convolutions: 



1. Superior or first occipitofrontal convolution, 0. F. includes or rather divides 



into F x superior frontal + anterior central A. C. 



2. Middle or second occipitofrontal convolution, 0. F 2 . includes F 2 middle 



frontal + posterior central P. C. 4- gyrus parietalis superior P 1 . 



8. Iilferior or third occipitofrontal convolution, 0. F. includes F 3 inferior 

 frontal + gyrus parietalis inferior P 2 P 2 ' {which equals P 2 siifra 

 marginal and P 2 ' angular gyrus). 



4. Mesial occipitofrontal convolution, M. 0. F. = Mesial occipitofrontal convo- 

 lution or gyrus fornicatus. 



OCCIPITAL LOBE. 



The occipital lobe is either entirely smooth, possessing, according to the classi- 

 fication of fissures adopted, no other fissures belonging to the second class, or it 

 becomes fissured by the formation of a secondary occipital arch 1 ' 2 ', which is a 

 repetition of the primary and belongs, therefore, properly speaking, to the third 

 group or sulci. (Owing to the important nature of this arch and its usual form, 

 it may be regarded as a whole and termed the sulcus occipitalis tri-radiatus) .. 

 It is well shown in the Chimpanzee, PI. XXXVIII, fig. 16, in Man, PI. XXXVI, 

 fig. 5, and in the Simiada?, PI. XXXVII, figs. 10 and 13, and PI. XXXVIII. fig. 

 5. It often separates into two portions which may be called sulcus occipitalis 

 primus and sulcus occipitalis secundus, PI. XXXVI, fig. 6, 0'' 1 ' and 2/ 2 '.. 

 These separate three occipital convolutions : — 



1. Gyrus occipitalis superior, S. Oc. 



2. " " medius, M. Oc. 



3. " " inferior, I. Oc. 



In the third division of fissures, the sulci, we find such furrows as the sulcus 

 pre-centralis, sulcus post-centralis, sulcus temporalis inferior of Ecker, etc. These 

 fissures as a rule, repeat the lines of fissuration of some secondary fissure, that is 

 run parallel with, and are of the nature of vegetative repetitions of it, produced 

 no doubt by the action of the same component forces as give rise to the line of 

 direction of the original fissure. They serve to give increased surface and a 

 special marking to the important and typical convolutions and so called lobules.. 

 They may be of primary or of secondary importance according to their constancy 

 of form and position. 



The fourth division or sulculi are usually repetitions of the lines of the 

 sulci or are small and inconstant fissures. The division included under the term 

 rami comprises branches of varying value, as for instance the ramus ascendens 

 of the Sylvian and constant branches of other important fissures. 



With regard to the manner of arrangement of the fissures and convolutions 

 around the fundamental furrows I have arrived at the following conclusions : 



1. The secondaiy fissures are related in a symmetrical manner to the primary.- 



