CORTICAL AND INTERNAL GREY SUBSTANCES. 561 



In the innermost grey layer the cells have similar characters, but often contain 

 pigmentary matter. Tubular fibres exist throughout : those of one set run parallel 

 with the surface, and at certain depths are more densely aggregated, so as to form 

 the before-mentioned white layers : they are also present in the intervening grey 

 strata, but there they are wider apart. The manner in which they begin and end is 

 not known ; it seems not improbable, however, that they are dependencies of the 

 commissural system of fibres. These stratified fibres, if they might be so called, are 

 intersected by another set of tubular fibres, which come from the central white 

 mass of the hemispheres, and run perpendicularly through the cortical substance, 

 becoming finer and spreading more out from each other as they approach the surface. 

 The further disposition of these central or perpendicular fibres is uncertain; 

 Yalentin describes them as forming terminal loops or arches, but this is denied by 

 Remak and Hannover. Remak states that they gradually disappear from view at 

 different depths, as they pass through the successive layers, the last of them vanish- 

 ing in the superficial grey stratum ; but he is unable to say positively how they 

 terminate. It sometimes seemed to him as if the last of them, after intersecting the 

 fibres of the deeper white stratum, became continuous with those of the outermost 

 layer ; but of this he by no means speaks confidently. Hannover maintains that 

 the perpendicular fibres are connected at their extremities with the nerve-cells in the 

 cortical substance. 



The grey matter of the lamina cinerea, tuber cinereum, and posterior perforated 

 spot, appears both in the base of the brain and in the floor of the third ventricle. 

 The lamina cinerea is connected externally with the grey matter of the anterior 

 perforated spot, and from that point a continuity of grey matter can be traced to 

 the swelling of the olfactory bulb. Thus also continuity is established between the 

 grey matter of the hemispheres and that of the interior of the brain. 



III. The grey matter of the interior of the cerebrum may be examined in the series 

 of its deposits from behind forwards. 



In the crura cerebri, the grey matter is collected into a dark mass, the locus 

 niger, which lies between the crust and the tegmentum, and is also diffused among 

 the fasciculi of the tegmentum ; below this it is continuous with that of the pons 

 and medulla oblongata, and through them with that of the spinal cord, as has already 

 been sufficiently described. In the upper part of each tegmentum is a round reddish 

 grey centre, the red centre of Stilling, the superior olive of Luys. 



In the centre of each of the corpora quadrigemina grey matter is also found ; and 

 this collection is stated by Huschke to be continuous below with the posterior cornu 

 of the grey matter of the spinal cord, posteriorly with that of the corpus dentatum 

 of the cerebellum, and anteriorly with the soft commissure, the septum lucidum, 

 optic thalami, and corpus callosum. Grey matter occurs also in the pineal gland, 

 and in the corpora geniculata. These last bodies appear to be_ appendages of the 

 optic thalami. 



The grey matter of the optic thalamus constitutes the principal bulk of that body ; 

 it is, however, partially divided into an inner and an outer portion, by white fibres 

 passing through it. 



The corpus striatum contains three grey centres. That which forms the intra- 

 ventricular portion of the body, and is connected inferiorly with the lamina cinerea, 

 and with that portion of the grey matter of the optic thalamus which is seen in the 

 third ventricle, is named the nucleus caudatus. The principal centre of the extra- 

 ventricular portion, named nucleus lenticularis, external and inferior to the nucleus 

 caudatus, is separated from that centre by the white substance of the fibrous cone, 

 which, as it passes outwards, appears, when cut across, as a broad white band extend- 

 ing from behind forwards, and traversed by striae of grey matter passing from one 

 centre to the other. Between the nucleus lenticularis and the island of Reil, which 

 lies opposite to it, there intervenes a thin lamelliform deposit of grey matter, the 

 nucleus tceniceformis (Arnold), or claustruin (Burdach), which, in a transverse section, 

 is seen as a thin line. The lenticular nucleus is continuous with the grey matter of 

 the anterior perforated space. 



The corpus striatum and optic thalamus contain cells very much like those of the 

 cortical substance. In the corpora quadrigemina there are larger cells, approaching 

 in size to those of the cerebellum, besides very small cells and nucleiform bodies. 

 The dark matter, forming the so-called locus niger of the cerebral peduncles, and 



