MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 



327 



convolution the obere Zug der hintern Centralwindimg ; he includes the superior 

 parietal under the name of the posterior central convolution. 



MOEPHOLOGY OF THE FISSURES AND CONVOLUTIONS OF THE OCCIPITAL LOBE. 



As we pass from the lower to the higher Simiadse and thence to the Anthro- 

 pidge or races of mankind, we find that the primitively smooth occipital lobe 

 becomes more and more complicated, until in the higher races it reaches its greatest 

 complexity. The chief and most interesting fact in the morphological evolution 

 of this region is that it takes place according to a regular and symmetrical plan, 

 which follows the lines laid down by the primary occipital arch ; and the fissures as 

 they appear are, or may be considered as vegetative repetitions of this primary 

 arch. They are, in fact, in appearance and relations a repetition of the first, and 

 they belong to the third class of fissures according to the classification adopted 

 4n this paper. Their relations to the first arch and to the fundamental structure of 

 the occipital lobe are shown in fig. 20, the two branches being marked respectively, 



O 1 ' and O 2 '. They constitute the 

 Fig. 20. secondary occipital arch, and it 



will be seen that not only is this 

 arch symmetrically related to the 

 primary arch but also to the two 

 extremities of the transverse cal- 

 carinefissure,arching around them 

 in a scroll-like manner, — within 

 the position of the scroll-like ex- 

 tremities of the primary occipital 

 arch. These two arches express 

 primitive morphological type of 

 the occipital lobe and by examin- 

 ing with attention fig. 5, Plate 

 XXXVII, it will be seen that on 

 the mesial surface this symmetri- 

 cally developed posterior extremi- 

 ty of the hemisphere is related in a regular and definite manner to the occipito-frontal 

 and occipito-temporal lobes. In this brain of Macacus nemestrinus the fissures have 

 been opened up in order to display more perfectly the symmetry of this region, and it 

 can be at once seen that the occipital lobe is symmetrically folded around the position 

 of the fissura calcarina, which corresponds to the position of the eminence found 

 within the posterior horn of the lateral ventricle known as the hippocampus minor. 

 From the position of the two extremities of the transverse calcarine fissure, both 

 the primary and secondary arches pass in a scroll or spiral-like turn forward toward 

 the apex of the occipital lobe, the ends of the primary arch being separated from each 

 other on the lateral surface by the small gyrus, x, (see fig. 20) or 4 (see plates), the 



41 JOUEN. A. N. S. PHILA., VOL. X. 



mof 



mot 



