CEREBRUM. 101 



acidulated with dilute acetic acid, and, after washing in pure water, stain it with iodine-green, 

 and mount it in dammar. The outer layer and Purkinje's cells of the grey matter are stained 

 red, and- the inner layer is stained green. 



THE CEREBRUM. 



PREPARATION. Prepare it in the same way as the cerebellum (p. 100), using the same 

 precautions both for hardening the tissue and for cutting it as indicated for the spinal cord 

 (p. 96). Select a frontal convolution of a human brain for examination. Stain the sections 

 with aniline blue-black, and mount them in dammar. 



Vertical Section of a Human Cerebral Convolution. EXAMINATION (L). Observe the shape 

 of a convolution, and contrast it with that of the cerebellum. Notice the pia mater surround- 

 ing the convolution, and sending fine processes carrying blood-vessels into the cortex. Notice 

 the deeply stained grey matter or cortex, and the white matter within. Examine the layers 

 of the grey matter from without inwards. It is possible to distinguish five layers, varying in 

 thickness and structural characters (Meynert). These layers are not accurately mapped off from 

 each other ; still they can be seen. It is to be remembered, however, that there are variations 

 in different parts of the cortex. In some places only four layers can be distinguished.- 



1. The outer layer contains few cells of any kind imbedded in a clear matrix. It occupies 

 about one-tenth of the entire thickness of the grey matter. 



2. This is about equal in thickness to the preceding, though it is easily distinguished by its 

 containing a large number of densely packed small pyramidal cells. Owing to the large 

 number of cells in this layer it always appears deeply stained. 



3. This layer is much wideband, owing to the cells occurring in it being placed well apart 

 from each other, it appears somewhat lighter than the second layer. It consists of large and 

 small pyramidal cells, so placed that their apices are directed towards the surface of the con- 

 volution, and their bases towards the white matter. 



4. This layer contains small irregular corpuscles with few processes. 



5. This layer is broader than the one above it, and contains similar corpuscles mixed with 

 a few fusiform cells. At its lower part it gradually shades into the white matter, which con- 

 sists of very fine medullated fibres, supported by neurogleia. {Indicate the general arrangement 

 of the cells in PI. XXIV., Fig. 3.) 



(H). Study in detail the various layers, and especially note the cells of the third layer. 

 The cells are distinctly pyramidal. Trace the long, branching process directed towards the 

 surface, and the branching processes from each angle of the base. Each cell has a central axial 

 cylinder-process. Each ganglion-cell lies in a lymph-space. It is to be observed, however, 

 that these cells only appear pyramidal when the plane of the section passes parallel to their 

 long axis. If cut transversely they appear triangular. {Indicate a nerve-cell in PI. XXIV., 



Fig. 4-T 



Select a blood-vessel of the grey matter, and observe its perivascular lymph-space. 



The processes of the cells are best seen in preparations which are only partially cleared up 

 under the influence of clove oil. This is a most important method of investigation. I have 

 often seen in this way delicate fibrils, not unlike elastic fibres, and which are not distinct when 

 the section is completely cleared up. 



ft.* 



