75 8 THE CEREBRAL CORTEX. 



of the cuneus. Monakow 1 limits the visual area to the cuneus, the lingual 

 lobule, and (probably) the two occipital gyri. The cuneus and lingual 

 lobule are especially connected with the corpus geniculatum laterale, from 

 which they receive fibres which run in the ventral part of the medullary 

 centre of the occipital lobe ; on the other hand, fibres pass from the cells 

 of the visual area by way of the optic radiations to the superior corpora 

 quadrigemina. All parts of the macula lutea are in man, according to 

 Monakow, represented in both hemispheres, and over the whole visual 

 cortex ; hence, if the whole visual area of one hemisphere is destroyed, 

 or even if the optic tract is completely degenerated, the macula lutea is 

 not completely blind in any part. 



According to Henschen, 2 the cortical centre for vision in man 

 (inclusive of colour vision) lies exclusively in the grey matter bounding 

 the calcarine fissure, 3 the upper lip of that fissure being connected with 

 the upper quadrant of the retina, the lower lip with the lower quadrant, 

 the macula lutea with the most anterior part of the area, and each 

 macula being represented in both visual areas. Henschen describes the 

 " visual " fibres of the optic tract as ending exclusively in the lateral 

 geniculate body, the destruction of which produces hemiopia. From 

 this fibres run in the ventral part of the optic radiations of Gratiolet to 

 the cortex at the calcarine fissure. The remainder of the occipital 

 cortex and the angular gyrus are considered by Henschen to be probably 

 connected with special visual apperceptions, as is instanced by word- 

 blindness accompanying lesions of these parts. 4 



Flechsig 5 1ms vshown that in man the fibres of the optic nerve become 

 myelinated later than those of most of the other senses, viz. in the course of 

 the first month of post-uterine life. Tracing them backwards, he finds the fibres 

 of the optic tract passing directly to the lateral geniculate body, and thence to 



1 Areh.f. Psychiat., Berlin, 1891, Bd. xxiii. S. 609; 1892, Bd. xxiv. S. 229. 

 " " Klin. u. anat. Beitr. z. Pathol, des Gehirns," Upsala, 1890-94 ; and Brain, London, 

 1893, p. 170 ; "Sur les centres opt. cerebraux," Internat. Med. Cong., Rome, 1891. 



3 The grey matter of the calcarine fissure, together with the immediately adjacent parts 

 of the cuneus and lingual lobule, is characterised by the development of a stratum of white 

 fibres in the middle of its thickness, which is known as the band of Gennari, as well as by 

 the thickness of the molecular layer, and the appearance of a very large number of stellate 

 nerve cells, which form a layer of considerable thickness in connection with the. band of 

 Gennari. This layer corresponds with the layer of granules in other parts of the cortex. 

 This part has been termed by Henschen the "cerebral retina" ; he supposes that visual 

 impressions are projected and received here, but are perceived elsewhere in the occipital 

 lobe, and perhaps also in the parietal lobe. The structure of the visual cortex in man has 

 been recently dealt with in a special treatise by Ramon y Cajal ("Die Schrinde," 

 Leipzig, 1900), who draws especial attention to the presence of many stellate cells in the 

 granule layer having descending instead of ascending axons. The fibres of the stripe of 

 Gennari constitute, in all probability, according to Cajal, the eventual endings of the 

 optic nerve fibres. 



4 See further, on visual representation in the cortex, Gowers, "Diseases of the Nervous 

 System," vol. ii. p. 142; Obersteiner, " Anatomy of Central Nervous Organs," p. 284; 

 Exner, "Untersuch. u. d. Local, der Functionenin d. Grosshirnrinde des Menschen," Wien, 

 1881 ; Allen Starr, Am. Joum. Med. Sc, Phila., 1884, vol. lxxxvii. p. 65 ; S^guin, Arch, de 

 neurol., Paris, 1886, p. 176 ; Nothnagel and Naunyn, "Ueber die Localisation der 

 Gehirnkrankheiten," Wiesbaden, 1887; Hun, Am. Joum. Med. Sc, Phila., 1887; Delepine, 

 Trails. Path. Soc. London, 1890, p. 2; J. Soury, "Les fonctions du cerveau," 1892; and 

 Rev. phil., Paris, 1895 and 1896 (see an account by Miss F. E. Welby in Brain, London, vol. 

 xix. p. 432) | also article "Cerveau" in Richet's "Diet, de physiol.," 1897, pp. 898-952 ; 

 Sachs, "Das Hinterhauptslappen," Leipzig, 1892 ; Donaldson, Am. Joum. Psychol., 1892, 

 vol. iv. No. 4; Ewens, Brain, London, 1893, vol. xvi. p. 475; Brissaud, Ann. d'ocul., 

 Bruxelles, 1893, tome ex. p. 321 ; Vialet, "Les centres cerebraux de la vision, etc., "Paris, 

 1893; and A rch. d'ophth,, Paris, tome xiii. p. 422; H olden, Areh.f. Ophth., Leipzig, Oct. 1896; 

 Sharkey, Lance', London, 1897, vol. i. p. 1399 ; W. Harris, Brain, London, 1897 ; vol. xx. 



5 "Localisation der geistigen Vorgiinge," Leipzig, 1896. 



