MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 



89 



6. The plis de passage inferieur interne (gyrus cunei), 1. Fig. 22, passes from 

 the cuneus to join the mesial occipitofrontal convolution, and corresponds morpho- 

 logically to the posterior portion. Z. of the mesial occipitotemporal convolution, 

 M.O.T., which should also be considered as a passage fold if the others are to be 

 regarded in that light. The accompanying diagrams will show that there are 

 seven of these roots of origin of the anterior convolutions of the occipital lobe 

 similarly related to the occipital lobe on the one hand and to the occipito-frontal 

 and temporal on the other. 



Fig. 21. 



Fig. 22. 



The deuxihne pli de passage externe, 3, unites the arch of the conjoined 

 superior occipito-temporal and inferior occipito-frontal, whilst each of the others 

 connects the remaining corresponding convolutions with the occipital lobe. They 

 are thus intimately related with the morphological type developed in this paper 

 and take their place as curiously developed parts of elements entering into this 

 plan. 



LOBULUS CENTRALIS. 



Most writers, as we have seen, consider this under the title of the central 

 lobe, but its structure and relations are manifestly so different from those of the 

 other lobes, that I prefer to consider it under the name, lobulus centralis, or 

 central cortical nucleus. It is closely related and is in direct connection with the 

 great ganglionic mass of the hemisphere, the corpus striatum, and is symmetric- 

 ally placed in its relations with the three lobes of the hemisphere. It is well 

 shown in its relations and external appearance in fig. 1. Plate XXXIX. as it 

 occurs in the human brain. It appears to be peculiar to the Primate brain 

 or at least it is but feebly represented in the brains of other orders of mam- 

 malia. In Man it contains three or four short convolutions or rather swellings, 

 the gyri breves of Gall and Arnold. It is concealed by the operculum in the 

 brain of the Caucasian and Mongolian, as far as observation has shown, but is 

 partly exposed in the brain of the Negro, a foetal peculiarity also shared by 

 some specimens of the Anthropoid apes, but absent in the Simiada^ generally. 



