THE BRA IX A XI) ITS MEMBRAXES. 777 



The aticemliti'/ parietal <-<>n>-<>hition is bounded in front by the fissure of Rolando, 

 behind by the ascending portion of the intraparietal and the post-central sulci. 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 generally above, the termination of 

 the fissure of Rolando. 



The mi / ///"/ purii-fiiJ convolution is bounded in front by the post-central sulcus, 

 which separates it from 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 connected 

 with 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 intraparietal 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 intraparietal 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 sub- 

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

 lies behind the lower end of the intraparietal sulcus and above the horizontal limb 

 of the fissure of Sylvius. It is connected, in front, with the ascending parietal 

 convolution beneath the intraparietal sulcus, and with the superior temporal con- 

 volution behind, around the posterior extremity of the fissure of Sylvius. The 

 other, the angular, is connected in front with the foregoing and 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 

 yyrus. 



The occipital lobe is triangular in shape and forms the posterior extremity of 

 the hemisphere. It rests upon the tentoriuin. Its external surface is bounded 

 in front by the external parieto-occipital fissure and a line drawn from the 

 extremity of this in the direction of the fissure across the outer surface of the 

 hemisphere. It is continuous below and in front with the temporal lobe, and 

 above and in front with the parietal. It is divided on the outer surface of the 

 hemisphere into three convolutions by two indistinct sulci the superior and 

 //* 1-,,-,-ijiitiiJ fill.-!. They are directed backward across the lobe, being fre- 

 quently small and ill-marked ; the superior is sometimes continuous with the 

 horizontal portion of the intraparietal sulcus. 



The x//y /''/ -i-'-ipital convolution is situated above the superior sulcus, and is 

 connected to the superior parietal convolution by the first annectant gyra*. 



The mi'ldle occipital convolution is situated between the superior and middle 

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

 'jiiriix. and to the middle temporal by the third annectant gyrus. 



The ////<//"/ o.v/y ////// r,, involution is situated below the middle occipital sulcus. 

 and is sometimes separated from the external occipito-temporal (fourth temporal] 

 convolution on the under surface of the hemisphere by an inconstant sulcus, the 



rior n>-i-ipital sulcus (posterior extension of third temporal sulcus; see next 

 page). The fourth annectant gyrus unites it with the third temporal gyrus. 



The temporal (temporo-sphenoidciT) lobe is that portion of the hemisphere which 

 is lodged in the middle fossa of the base of the skull. In front and above it is 



other of these different parts of the intraparietal sulcus. but that the one in which the three parts of 

 the sulcus are confluent is by far the most constant condition. Sometimes, however, the three parts 

 of the siilcus may be all separate, or the ramns horizontalis confluent with the ramus verticalis infe- 

 rior, 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 to the lower end 

 of the ramus verticalis superior, while the lower vertical limb is separate. The connection which 

 sometimes exists between the intraparietal sulcus and the occipital lobe he calls the ramus occipitfiJi*. 

 In the majority of cases, however, the occipital ramus is separated from the main portion of the infra- 

 parietal sulcus by a superficial or deep bridging convolution (Journal of Anatomy and Physiology, vol. 

 xxiv. part ii. p. 135). 



