HEMISPHERES OF THE BRAIN. 651 



The ascending parietal convolution is bounded in front by the fissure of 

 Rolando, behind by the ascending portion of the intra-parietal sulcus and by the 

 post-central sulcus. It extends from the great longitudinal fissure above to the 

 horizontal limb of the fissure of Sylvius below. It lies parallel with the ascending 

 frontal convolution, with which it is connected below, and also, sometimes, above 

 the termination of the fissure of Rolando. 



The superior parietal convolution is bounded in front by the post-central 

 sulcus, which lies between it and the previous convolution, but with which it is 

 usually connected above the upper extremity of the sulcus ; behind, it is bounded 

 by the external parieto-occipital fissure, below the termination of which it is 

 joined to the occipital lobe by a narrow convolution, the first annectant gyrus ; 

 below, it is separated from the inferior parietal convolution by the horizontal 

 portion of the intra-parietal sulcus ; and above, it is continuous on the inner 

 surface of the hemisphere with the quadrate lobe. 



The inferior parietal convolution is that portion of the parietal lobe which is 

 situated between the ascending portion of the intra-parietal sulcus in front, the 

 horizontal portion of the same sulcus above, the horizontal limb of the fissure of 

 Sylvius below, and the posterior boundary of the parietal lobe behind. It is 

 divided into two convolutions by an indistinct groove. One, the supra-marginal, 

 lies behind the ascending part of the intra-parietal sulcus and above the horizontal 

 limb of the fissure of Sylvius, over the extremity of which it arches. It is con- 

 nected in front with the ascending parietal convolution below the intra-parietal 

 sulcus, and behind with the superior temporal convolution round the posterior 

 extremity of the fissure of Sylvius. The other, the angular, is united anteriorly 

 with the foregoing, while posteriorly it is continuous with the middle temporal 

 convolution by a process which curves round the superior temporal or- parallel 

 sulcus. It is connected with the occipital lobe by the second annectant gyrus. 



The internal or mesial surface of the parietal lobe is continuous with the 

 external surface over the upper edge of the hemisphere. It is of small size, and 

 forms one square-shaped convolution, which from its shape is termed the quadrate 

 lobe. From its situation above the cuneate lobe it is sometimes named precuneus. 



3. The Occipital Lobe. The occipital lobe is divided on its external surface 

 into three convolutions by two indistinct sulci, the superior and middle occipital 

 sulci. They are directed backward across the lobe, being frequently small and 

 ill marked ; the superior is sometimes continuous with the horizontal portion of 

 the intra-parietal sulcus. 



The superior occipital convolution is situated above the superior sulcus, and is 

 connected to the superior parietal convolution by the first annectant gyrus. 



The middle occipital convolution is situated between the superior and middle 

 occipital sulci, and is connected to the angular convolution by the second annectant 

 gyrus, and to the middle temporal convolution by the third annectant gyrus. 



The inferior occipital convolution is situated below the middle occipital sulcus, 

 and is sometimes separated from the external occipito-temporal convolution on 

 the under surface of the hemisphere by an inconstant sulcus, the inferior occipital 

 sulcus. It is connected to the inferior temporal convolution by the fourth annec- 

 tant gyrus. 



The internal or mesial surface of the occipital lobe presents a triangular con- 

 volution, which is known as the cuneus or cuneate lobule. It is situated between 

 the internal parieto-occipital and calcarine fissures, which, as already mentioned, 

 meet some distance behind the posterior extremity of the corpus callosum. 



the three parts of the sulcus may be separate, or the ramus horizontalis confluent with the ramus 

 verticalis inferior, the ramus verticalis superior remaining separate ; or, again, the vertical limbs may 

 be confluent and the horizontal limb separate ; or, finally, the ramus horizontalis may be joined 

 the lower end of the ramus verticalis superior, while the lower vertical ramus is separate. Ihe pro 

 longation of the intra-parietal sulcus into the occipital lobe, which sometimes exists, he cai 

 ramus occipitalis. In the majority of cases, however, the occipital ramus is separated from the 

 portion of the intra-parietal sulcus by a superficial or deep bridging convolution. (Journal of Am 

 and Physiology, vol. xxiv., part ii., p. 135.) 



