612 DR JAMES W. DAWSON ON 



called satellite cells or " Trabantzellen " — and around the vessels. These elements, 

 together with arteries, veins, and a fine capillary network, constitute the grey 

 matter of the cortex. The specific glia fibrils vary much in amount in the different 

 layers. In the marginal zone and amongst the tangential fibres they are abundant, 

 but from this downwards they rapidly decrease in amount, but in the transition 

 between white and grey matter they are again abundant. On the other hand, the 

 protoplasmic glia meshwork is apparently equally developed at all levels. Radial 

 glia septa, such as are found in the cord, are never present in the cortex. The 

 nuclei in the grey cortex are small and round, 5 to 7m in diameter, or flattened, and 

 have a dense chromatin content in the form of fine granules. Larger and lighter- 

 stained nuclei are also met with, and both types have, with certain stains, fine 

 thread-like processes, which ramify and anastomose with each other. 



We have stated that one portion of the proliferated glia cells both in the white 

 and grey matter probably form the first fat granule cells. This double function of 

 the neuroglia cells, that of fibre-formation and phagocytosis, has been emphasised by 

 Nissl, Marinesco, and Ford-Robertson. The increasing zone of protoplasm around 

 the nucleus becomes gradually laden with granules, which often outline the cell body 

 and its processes — at first spindle-shaped, then star-shaped, and gradually becoming- 

 rounder till the cells are set free in the glia reticulum (figs. 18-20). These glious 

 granular cells have a lattice or " Gitter " structure in their protoplasm, in prepara- 

 tions in which the fat granules have been dissolved out (figs. 9, 10). They emigrate 

 from the tissue, or rather are carried along with the lymph stream, and are found 

 later in the adventitial spaces of the blood-vessels and there give up their contents, 

 or are carried still further on. This evolution may be traced beautifully in the 

 advancing zone of an area in the white matter where the nerve fibres are cut 

 longitudinally. Here the pre-existing small glia cells, lying far into the normal 

 myelinated tissue, may be found proliferating and undergoing the changes described 

 above. In the cortical grey matter this evolution is slower, and the commencing 

 granule formation in the " Trabantzellen" is well brought out in fig. 396. 



4. Blood-vessels ; Lymphatics ; Cell Elements in Vessel Walls. 



(a) Blood-vessels. — Note on the normal structure of the vessels of the central 

 nervous system. 



The arterial vessels of the cerebral cortex arise altogether from the pia. Short 

 radial branches, referred to as "cortical" vessels, pass into it perpendicular to the 

 surface, and soon after their entrance break up into the very smallest arterioles and 

 capillaries. The outermost layers of the cortex are supplied, not by lateral branches 

 from the larger of those radial arteries, but by a special system of very short vessels, 

 which break up into a capillary network in the first and partly in the second cortical 

 layers. One division — of longer radial branches, referred to as medullary — penetrates 



