MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 303 



1. The calloso-marginal with its various vegetative separations and repetitions, 

 among which are the so-called transverse furrow or sulcus of the gyrus paracen- 

 tral of Betz, J, PI. XXXIV, fig. 2 and Pis. XLI and XLII, fig. 2; and the sulcus 

 of the precuneal lobule, m.o.f. 



2. The fissure between the two internal pits de passage when these are 

 present. 



MESIAL OCCIPITOFRONTAL CONVOLUTIONS. 



The mesial occipito-frontal fissure separates, as may be well seen in fig. 2, 

 Plates XLII and XLIV, two convolutions. Of these, I shall call the upper for the 

 present the marginal mesial occipito-frontal, whilst the lower, M. 0. F., evidently 

 corresponds to M. 0. T. I therefore designate it as the mesial occipito-frontal 

 convolution. This convolution posteriorly is connected with the occipital lobe by 

 means of the gyrus cunei (internal inferior pit de passage), Plate XLII, fig. 2, and 

 proceeds forward surrounding the corpus callosum to the end of the hemisphere. 

 Posteriorly below the splenium it becomes continuous with the gyrus hippocampi. 

 It corresponds to the gyrus fornicatus of other writers. 



Not only do I believe that this method of considering the mesial surface of 

 the hemisphere is the most convenient, but I will endeavor to show that this 

 nomenclature represents the nature of the arrangement of these parts, and at 

 the same time brings the occipito-frontal portion into harmony with that of 

 the occipito-temporal, parts which I believe are morphologically homologous. 



Occipitofrontal Lobe (Lateral Portion). 



The lateral portion of the occipito-frontal lobe has been considered hy all 

 recent writers as consisting of two distinct lobes, the frontal and parietal. We have 

 already given reasons for dissenting from this view, yet it will be convenient to divide 

 it into two regions, a frontal and a parietal, separated from each other by the well 

 marked fissura centralis (Rolando) . Anatomists are not at all agreed as to the poster- 

 ior limitations of the frontal from the parietal portion. Pansch and Ecker place all 

 that portion of the hemisphere anterior to the central fissure in the frontal lobe. 

 Others, including Bischoff, Huxley and the English anatomists who have written 

 on this subject, place the posterior boundary of the frontal lobe directly in front of 

 the anterior central convolutions, A. C, so that both of the convolutions surrounding 

 the central fissure, C, are placed in the parietal lobe. With regard to this point Gratio- 

 let expresses himself as undecided, although in his writings he places the boundary 

 in front of the anterior central convolution or premier pli ascendant, as he terms 

 it. Regarding as I do, the separation of the upper anterior portion of the brain 

 into the frontal and parietal lobes as of secondary morphological value, and its 

 chief use for convenience of description, the division adopted by Pansch and Ecker 

 appears to me to be in every respect preferable to that of the other writers before 

 mentioned. The central fissure forms a fixed and and definite separation, while 



38 JOURN. A. N. S. PHILA., VOL. X. 



