120 Visuo-Sensory and Visuo-Psychic Areas [CHAP. 



in like manner as this lamination shuns the limbic wall so also it avoids the parieto- 

 occipital fissure ; thus on inspecting the floor of the last-named sulcus at the point where 

 it approaches the calcarine, it may be observed that a calcarine type of cortex covers the 

 lower but not the upper aspect of the gyrus cunei of Ecker (i.e. the annectant gyrus, which, 

 when the fissure is opened out, is seen extending from the apex of the cuneus across the 

 floor of the parieto-occipital fissure to the opposite bank). 



But as soon as the cuneus is reached this type of cortex at once passes across the 

 floor of the calcarine fissure and ascends the upper wall, and all along this hinder portion 

 of the fissure the special lamination coats both its walls (including the anterior and posterior 

 cuneo-lingual annectant gyri), it also spreads for a varying distance roughly speaking about 

 1 cm. on to the free surface of the cuneus above, and of the lingual lobule below. On 

 the cuneus, the cuneal sulcus (parallel cuneal sulcus of Bolton 1 ), a small fissure running 

 parallel with the posterior calcarine fissure, commonly forms a boundary, but as the position 

 of this fissuret is not constant it must not be regarded as a fixed limit. On the lingual 

 side the boundary is not always determined by sulci, although it may touch and even cross 

 the hinder limb of the collateral fissure, when this sulcus happens to approach the calcarine ; 

 accordingly I do not think that Bolton is correct in describing the posterior division of the 

 collateral fissure as a boundary. More frequently the area comes into relation with a small, 

 unnamed and shallow sulcus which lies longitudinally on the gyrus lingualis, midway between 

 the calcarine and collateral fissures ; a sulcus which is not to be confounded with the hinder 

 portion of the collateral fissure, although it often anastomoses with it, and one which for 

 explanatory purposes I shall refer to as the lingual sulcus-. But this sulcus again is inconstant 

 in position and must also not be looked upon as an invariable limit. 



When we reach the forked extremity of the posterior calcarine fissure, the fissura extrema 

 of Seitz, the area attains its maximum dimensions, measuring about 3 cm. in the vertical 

 direction ; and, as proving the intimate relation which the area bears to the calcarine fissure, 

 it is interesting and important to notice that the width of this posterior expansion is directly 

 proportionate to the length of the fissura extrema ; thus, if the fissura be unusually long, 

 the area will be correspondingly broad ; and if, as sometimes happens, one limb of the fork 

 be shorter than the other, the extent of the area will be curtailed on that side ; and while 

 as a rule the area taken altogether is usually of pear shape, variations in the direction 

 and curves of the calcarine fissure and in the length of its two posterior prolongations, may 

 give rise to all sorts of variations in the boundary line. 



Concerning the distribution of the area on thr postero-lateral face of the hemisphere 

 it is important that this should be specially referred to, because when we come to study 

 the distribution of the area in the higher ape, we shall find that its extent is very different 

 from that which obtains in the human being. 



Now in man, only a small portion of the area is found on the postero-lateral surface. 

 In a view of the lateral aspect of the hemisphere the field is just visible as a narrow 

 crescent peeping round the tip of the occipital pole, and viewed in full from the occipital 

 aspect it is not usually continued outwards for a distance of much more than 1 cm. And 

 close examination will invariably show that the lateral limit runs in line with and bears 

 a direct relation to the length and position of the fissura extrema of Seitz, again substantiating 



1 Elliot Smith, who appears not to have read Bolton's paper, calls this the sulcus limitans superior areae striatae. 

 - This sulcus has been recognised by Elliot Smith and named the sulcus limitaus inferior areae striatae. 



