STRUCTURE OF THE LOBES OF THE CEREBRUM. 391 



occur here as the third layer ; nevertheless this thick and 

 important formation is subdivided, by the intercalation of two, 

 poorly provided with corpuscles, intermediate granule layers, 

 into a zone composed of five layers ; so that the granule-like 

 formation of the first-named type occurs three times. The 

 fusiform corpuscles succeed to the innermost granule layer. 



The cortex is here consequently divided into eight laminae. 

 The two intermediate granule layers, with sparsely scattered 

 granules, here coalesce to form an incomparably sharply defined 

 white layer, in consequence of the invariable absence of pigment, 

 from which, on account of its tenuity, the middle granule layer 

 is indistinguishable. In this thinly celled region a few pyra- 

 midal corpuscles, either isolated or more rarely accumulated into 

 small groups, are found, of immense size, being at least twice 

 as large as those of the cornu Ammonis formation (solitary 

 cells). The brain of Monkeys, which is distinguished by ex- 

 cessive development of the occipital lobes, contains this type 

 of tissue in much greater abundance than the human brain. 



The formation presented by the summit of the occipital region has 

 been taken by Clarke as the starting-point of his researches on the 

 cortex of the cerebrum, and lie gives an accurate description of the 

 two thinly corpusculated layers. But since, like other authors, he has 

 not distinguished between the granule-like and fusiform formations, 

 as constituting separate layers, he fuses the external and internal 

 granule formation with the adjoining pyramids and spindle-shaped 

 bodies, and counts only six cortical layers, instead of eight.* 



3. In the type of the Sylvian fissure, the third form of the 

 cells of the cortex, the fusiform cells, predominate, forming the 

 claustrum and amygdaloid nucleus. The claustrum, as a dis- 

 tinct lamina of the innermost cortical layer, and divided from 

 the lenticular nucleus by the thin medullary lamina of the 

 external capsule (figs. 233, 243 245, Cl), lines the con- 

 volutions of the island, following ina fan-1 ike manner their 

 infections. Beyond the limits of the island it curves 

 round into the cortical wall of the Sylvian fissure above, into 

 the overhanging parietal (klapp-deckel), and below into the 



* [This is evidently an error ; Dr. Clarke was the first to describe eight 

 layers in the cerebral convolutions. Proceed. Roy. Soc., Vol. xii., No. 57. 

 TRANSLATOR.] 



