THE VISUAL AEEAS AND FIBKE-TKACTS. 



659 



a very distinct white line or stria, which was first noticed by Gennari in the 

 year 1776. 



If this visual receptive area striata of the occipital cortex is excised and spread 

 out in one plane, it will be found to present an elongated ovoid form and a super- 

 ficial extent of about 3000 sq. mm. (varying in different brains from about 

 2700 to 4000). The narrow extremity of the oval is placed a short distance 

 behind and below the splenium of the corpus callosum ; and from this point the 

 area extends horizontally backwards to the occipital pole, or even beyond it on to 

 the lateral aspect of the hemisphere. In the course of development this area 

 striata becomes folded along its axis during the sixth month, and the furrow thus 

 formed is called the sulcus calcarinus. This name was applied to the furrow by 

 Huxley because its deep anterior part indents the whole thickness of the medial 



4 Hubstantia 



perforata 

 i~~ anterior 

 r ,m|| Optic tract 



- - (cut) 



__ jj _J| Basis pedun- 



* culi cerebri 

 -$-. -~,^~ Optic tract 



Corpus 



geniculatun 



laterale 



^~ - Fascia dentata 



_ Isthmus gyri 

 cinguli 



-Area striata 



Lunate sulcus 



FIG. 586. DIAGRAM OF THE CENTRAL CONNEXIONS 

 OF THE OPTIC NERVE AND OPTIC TRACT. 



FIG. 587. A SLIGHTLY OBLIQUE (ALMOST HORI- 

 ZONTAL) SECTION THROUGH A CEREBRAL HEMI- 

 SPHERE IN THE PLANE OF THE OPTIC TRACT 

 AND RADIATION. 



wall of the hemisphere, and the swelling so produced in the posterior cornu of the 

 lateral ventricle was supposed by the older .'anatomists to resemble a cock's spur, 

 and was hence called calcar avis (see Fig. 566, p. 637). 



The anterior part of this furrow is much deeper, more constant in form and 

 position, more precocious in development, and phylogenetically much older than 

 the posterior part. As it is the part of the sulcus which gives rise to the calcar avis, 

 it is the true calcarine ; while the newer, shallower posterior part is wholly on the 

 caudal side of the calcar avis, and is called, sulcus calcarinus posterior. If the 

 area striata is prolonged on to the lateral surface, it also may become folded in the 

 line of its axis, and so give rise to a sulcus calcarinus lateralis. 



There is a fundamental distinction between the calcarine sulcus and the posterior 

 calcarine in their t relations to the area striata. For the stria of Gennari is 

 found only in the inferior wall of the sulcus calcarinus, which is therefore a sulcus 



43 a 



