SEC. 6. ON SOME HISTOLOGICAL FEATURES OF 



THE BRAIN. 



647. The white matter of the brain, as we have already 

 said, like that of the spinal cord consists of medullated fibres, of 

 various sizes, imbedded in neuroglia and supported by septa of 

 connective tissue derived from the pia mater. Save that cells, or 

 even groups or rows of cells, for the most part small cells, about 

 many of which it may be debated whether they are nerve cells or 

 neuroglia cells, are frequently seen between the fibres and bundles 

 of fibres, the white matter of the brain seems essentially identical 

 with that of the spinal cord. 



The grey matter of the brain in general also corresponds to the 

 grey matter of the cord in consisting of branching nerve cells, fine 

 medullated fibres of peculiar nature, non-medullated fibres and 

 fibrils, with a few ordinary medullated fibres, all supported in 

 neuroglia. 



The ' central ' grey matter is extremely like that of the cord 

 except that the nervous elements are imbedded in a relatively 

 larger quantity of neuroglia. Immediately underneath the epi- 

 thelium lining the several ventricles and the aqueduct, the 

 neuroglia is especially developed, forming a distinct layer which 

 may be regarded as a continuation of the central gelatinous 

 substance of the spinal cord, and which with the epithelium 

 overlying it forms what is known as the ependyma. The ' nuclei ' 

 of the cranial nerves are as we have seen comparable to the 

 groups of nerve cells in the spinal cord. 



A great deal of the grey matter of the brain may be spoken of ' 

 as more ' diffuse ' or ' scattered,' more broken up by bundles of 

 fibres than is the case in the spinal cord. The 'reticular formation' 

 of the bulb, and of the tegmental region, is an extreme form of 

 this diffuse grey matter. And even in such collections of indu- 

 bitable grey matter as the corpus striatum, optic thalamus and 

 the like, the pure grey matter, if we may use the term, is much 

 more interrupted and broken up by conspicuous bundles of white 

 fibres than is the case in any region of the spinal cord. In the 



