of the Visual Area of the Human Cerebral Corte>. 217 



(3) The approximate outline of this area is consequently pear 

 shaped with the apex anteriorly and the thick end at the pole of the 

 hemisphere. 



(4) The area is much decreased in extent, but not in distribution, in 

 cases of old-standing optic atrophy. 



(5) In anophthalmos the area is much contracted as regards both 

 extent and distribution. It occupies the usual position in the stem of 

 the calcarine fissure, but only extends backwards as far as the posterior 

 cuneo-lingual annectant, and it is confined to a portion of the inferior 

 lip of the fissure and to the cortex between this and the collateral 

 sulcus. 



The General Histology of the Cortex Cerebri in the Region of the Calcarine 



Fissure. 



(1) The following classification of layers has been adopted for the 

 purposes of micrometer measurements : 



(rt) The cortex of the area of special lamination which has just been 

 described. 



I. The superficial layer of nerve fibres. 



II. The layer of small pyramidal cells. 



Ilia. The outer granule layer. 



Illb. The middle layer of nerve fibres, or line of Gennari. 



Illr. The inner granule layer. 



IV. The inner layer of nerve fibres. 

 V. The layer of polymorphic cells. 



(&) The cortex surrounding the area of special lamination. 



I. The superficial layer of nerve fibres. 

 II. The layer of small and large pyramids. 



III. The layer of granules. 



IV. The inner layer of nerve fibres. 



V. The layer of polymorphic cells. 



At the junction of these two varieties of lamination an abrupt 

 change takes place, the line of Gennari suddenly ceasing, and the outer 

 granule laj^er joining the inner one, the conjoined layer being approxi- 

 mately of the thickness of the former outer layer. 



(2) The average of very numerous micrometer measurements of the 

 cortex of the area of special lamination and of the neighbouring con- 

 volutions gives the following results : 



(a) In the area referred to, in cases of old-standing optic atrophy, 

 the line of Gennari is decreased nearly 50 per cent, in thickness, 

 and the outer granule layer more than 10 per cent. 



