344 MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 



of the occipito-temporal is little disturbed in all its different stages of develop- 

 ment. The occipito-frontal, however, undergoes as we have seen, marked morpho- 

 logical changes ; still the primitive similarity, the different stages of the changes 

 and the forces at work to produce the disturbance are quite evident, and we are 

 still able to point out and* compare the further evolved and more differentiated 

 portions of the parietal region with the original potential type, and thus with the 

 corresponding portions of the occipito-temporal lobe. 



I have, therefore, in Plate XLIV colored the homologous portions with the 

 same tints; at once the perfect symmetry of the convolutional configuration is 

 evident to the eye, and the entire morphological type or plan proposed in this paper 

 can be readily applied to the study of the fissures and convolutions as represented 

 in the various plates. 



Viewed in this way, the arrangement of the convolutions in Man and the 

 Simiadse becomes so clear, that at a glance one can see, recognize, and remember the 

 entire cerebral conformation of any individual brain that may be under examination, 

 and any special peculiarities that may exist at once become marked and prominent. 

 Without the aid of this morphic conception the cerebral surface presents a confused 

 mass of isolated convolutions, lobules, fissures, sulci and sulculi, which it is impos- 

 sible to put together as a whole. It will thus be seen, that so far from the convolu- 

 tions being a bundle without a system as was thought by anatomists, even up to 

 quite recent times, and due to an irregular mechanical packing as one would 

 crumple a surface simply as a convenience for storing it away, they are produced 

 by the action of forces that are perfectly fixed, definite and regular. In other words, 

 the cerebral hemispheres are nervous buds, and like all other organic buds they 

 develop symmetrically, and the type of fissuration is due to the resultant forces pro- 

 duced by the interaction of the growth forces of the hemisphere combined with the 

 pressure forces of the less rapidly expanding but symmetrically developing cavity of 

 the skull. The question as to which of these two series of forces is most potent in 

 its differential action in producing fissuration it is hard to answer, but it would ap- 

 pear that during the earlier and even to the quite late stages of development it is 

 the brain which modifies the shape and structure of the skull rather than the 

 reverse, and that finally, as the skull grows more and more rigid, its influence is 

 shown by the increasing tortuosities and pushing out of place of previously existing 

 parts. Evidence corroborative of this is shown in the structure of the occipital lobe, 

 which being a late evolution is exposed to a more rigid environment during the pro- 

 gress of its final differentiations. 



NOMENCLATUEE. 



The nomenclature, as given by preceding writers, can still be retained, the re- 

 lations to the naming of the elemental parts entering into the morphological type as 

 advocated in this paper, being as follows, and may be readily compared by referring 

 to Plates XLII and XLIV. 



