420 THE BRAIN 



separates the margins of the fissure he will be able to con- 

 vince himself that the union of the two fissures occurs only 

 near the surface, and that the lower end of the deep part of 

 the parieto-occipital fissure is separated from the calcarine 

 fissure by a submerged ridge called the gyrus cunei. 



Fissura Calcarina. The stem or anterior part of the 

 calcarine fissure has already been seen on the inferior surface 

 of the hemisphere (p. 413). It crosses the medial occipital 

 border and joins the parieto-occipital fissure on the medial 

 surface of the occipital lobe. Then it passes backwards to 

 the occipital pole, round which it turns ; and it ends, on the 

 supero-lateral surface of the occipital lobe, in a terminal 

 bifurcation. If the dissector separates the margins of the 

 fissure he will find that, immediately behind its union with 

 the parieto-occipital fissure, a submerged ridge, the cuneo- 

 Hngual gyrus, separates the anterior from the posterior portion 

 of the calcarine fissure. The ridge is an indication that the 

 two parts of the calcarine fissure arose separately and became 

 combined at a later period both ontogenetically and phylo- 

 genetically. 



At this stage the dissector should make a frontal section 

 through the posterior part of the right occipital lobe, and 

 then examine the surface of the section of the grey matter in 

 the region of the posterior part of the calcarine fissure. If 

 the brain substance is in a state of good preservation he will 

 find a distinct white line, called the stria Gennari, which cuts 

 the grey matter into inner and outer parts, and which is not 

 present in the neighbouring regions. The portion of the 

 cortex marked by the line is called the area striata ; it is the 

 visual area of the cortex, and the line indicates that the portion 

 of the cortex in which it lies is associated with sight. It is 

 found in both walls of the posterior part of the calcarine 

 fissure and the adjacent parts of the cuneus and the lingual 

 gyrus which bound the fissure, but it occurs only on the 

 lower lip of the anterior part of the calcarine fissure, which is 

 situated, therefore, on the boundary line between the visual 

 and non-visual portions of the cortex. 



Sulcus Corporis Callosi. The callosal sulcus runs round 

 the convex outline of the corpus callosum, separating the 

 corpus callosum from the gyrus cinguli. 



Sulcus Cinguli, The sulcus cinguli runs parallel with the 

 callosal sulcus and is separated from it by the gyrus cinguli. 



