40 



Lewis and Clarke on the Cortical Lamination [Jan, 24, 



delicate protoplasmic investment. These cells include one, two, or 

 three nuclei, and assume a spheroidal or flask-like configuration in 

 situ; wheu, however, seen near the frayed-out margin of a teased 

 preparation, they are found to give off numerous radiating processes. 

 Aniline black (for which nervous elements have a great affinity) stains 

 their nuclei, investing protoplasm and its extensions so uniformly and 

 faintly, that it is with some difficulty they are recognised, complete 

 differentiation from the faintly-tinted matrix being scarcely attainable. 

 In form, reaction to staining agents, and still more as regards their 

 modifications by disease, they are undoubtedly proved to be connective 

 elements. We find occasionally that these elements proliferate freely, 

 assume the most quaint forms, and produce a dense matting of fibres. 

 Such a condition, truly a sclerosis, is figured in a paper recently con- 

 tributed to the Royal Society by one of the authors.* No other 

 cellular elements appear in the first layer of the cortex : the angular 

 and fusiform nerve-cells alluded to by some writers have had no 

 existence in specimens we have examined by the fresh and hardened 

 methods. They are probably elements of the connective group, pos- 

 sibly identical with the larger nucleated bodies just described, the 

 appearance of which is greatly altered by the methods of preparation 

 employed. The elements found in the first layer, therefore, are neu- 

 roglia corpuscles and perivascular cells. Both varieties are shown in 

 the drawings accompanying this paper. (Vide Plate 1, First Layer.) 



Second Layer. — This consists of a series of closely aggregated pyra- 

 midal and oval cells, of small size, w T hose apical processes are arranged 

 radially to the surface of the cortex. Numerous other processes arise 

 from the basal angles, and radiate outwards and downwards from the 

 cell, including an extensive area in their distribution. Their mea- 

 surements vary from to 23/a in length, and from 6/ti to 9/< in 

 breadth. Their nucleus is comparatively of large size, often measuring 

 4/* to 6 a in diameter, sometimes assuming the pyramidal form of the 

 enclosing cell, when it may attain a length of 9/i. With the exception 

 of their pigmy size and extremely crowded aggregation, no differences 

 are apparent between them and the larger elements of the third layer. 

 (Vide Plate 1, Second Layer.) 



Third Layer. — The reddish-grey band coinciding with the second 

 layer, as seen by naked-eye examination, appears abruptly marked off 

 from the pale layer subjacent to it. On microscopic examination, 

 however, it is found that the line of demarcation can be only approxi- 

 mately obtained, as the elements of both overlap each other very 

 irregularly. The distinction between these two layers near their 

 common boundary must depend upon a two-fold condition, viz., the 

 gradual increase in size of the elements of the third layer and their 

 * " The Relationships of the Nerve-cells of the Cortex to the Lymphatic System of 

 the "Brain." By Bevan Lewis, Proc. Eoy. Soc, Sept., 1877. 



