THE HISTOLOGY OF DISSEMINATED SCLEROSIS. 613 



further down and supplies the superficial portion of the subcortical white matter. 

 The larger portion of the cortical white matter and the basal ganglia are supplied 

 by central arteries, which arise from the circle of Willis : their terminal branches 

 ramify on the surface of the ventricles (Borst). One division of the veins likewise 

 passes to the pia, and another, that draining the central white matter and basal 

 ganglia, joins the great veins of Galen beneath the splenium of the corpus callosum. 

 Numerous venous branches can be recognised, immediately sub-ependymal, coursing 

 mostly obliquely towards this point, and grouped especially around the posterior horn 

 of the lateral ventricle. In the spinal cord the white columns are supplied by vessels 

 radiating from the pia, and the grey matter by vessels passing in from the anterior 

 fissure. The transition zone between white and grey matter receives its blood- 

 supply from the terminal branches of both central and lateral vessels. The lateral 

 vessels, as they penetrate the cord, run at first almost in the transverse section of the 

 cord ; many lateral transverse branches are given off, but the majority widen out 

 in vertical directions. These vertical branches, on account of their small calibre, 

 represent terminal vessels, pre-capillary arterioles, and capillaries, and may be traced, 

 in longitudinal section, for long distances. In consequence of this arrangement, the 

 areas supplied by the radial vessels and their lateral branches would, therefore, have 

 a wedge-shaped form, with base on the surface of the cord, and those supplied by 

 the vertical branches must have a shape in the long axis of the cord. 



The discrimination, in individual sections, of small arteries and veins is by no 

 means always easily made, and, when a condensation of the vessel wall occurs in 

 sclerotic tissue, is impossible. As in other tissues the venous walls are thinner, 

 contain irregularly distributed muscle cells and adventitial nuclei, but small veins 

 proceeding from capillaries cannot be distinguished from pre-capillary arterioles. 

 It is generally taught that no elastic lamina is present in the arteries and arterioles, 

 but Schroeder and Lapinsky state that a very delicate elastic membrane can be 

 recognised even in the capillaries, and that elastic fibres are present in the media and 

 the adventitia, wherever a distinct adventitia can be found. With Weigert's elastic 

 stain the capillary walls certainly stain sharply and frequently with a double contour, 

 which some have looked upon as the expression of a rudimentary elastic membrane. 

 It is generally admitted that even the capillaries have traces of an adventitia, the 

 nuclei of which are found only at intervals. The capillaries, therefore, consist of an 

 endothelium and traces both of an elastica and an adventitia. In pre-capillary 

 arterioles we get, in addition, detached muscle cells, which in the larger arterioles 

 form a layer of circular cells. Ford-Robertson states that by far the most 

 important feature in the structure of the intracerebral vessels, in relation to the 

 physiology of the cerebral circulation, is the remarkable development and the highly 

 elastic character of their adventitia, which invests not only the arterioles but also 

 venules and capillaries. The capillaries of the central nervous system, therefore, 

 unlike the capillaries of most other organs, possess an adventitia, the fibres of which 



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