INTEPwNAL STRUCTURE. 563 



meclullated nerve-fibres, arranged in interlacing bundles, which give 

 origin to the filaments that pass from the bulb to the nose. The grey 

 substance which lies between this layer and the lower medullated layer 

 contains numerous large granules and small angular and branching 

 nerve-cells. The granules are most abundant in the upper portion, 

 where they are arranged in flat groups ; the nerve-cells exist chiefly 

 in the lower part, contiguous to the gelatinous nerve-fibres, which pro- 

 bably arise from them. 



The grey matter of the anterior perforated spot is continuous 

 above with that of the corpus striatum and lenticular nucleus. Thus 

 also continuity is established between the grey matter of the surface 

 and that of the interior of the brain. 



(C.) GREY MATTER OF THE INTERIOR. — This 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 ; it extends through 

 the whole width of the crus, and from the anterior edge of the pons to 

 the corpora albicantia, and is continuous behind with the grey matter 

 of the pons and medulla oblongata. It consists of nerve-cells, of various 

 form, about x-\7oth of an inch average diameter, somewhat smaller than 

 those of the locus coeruleus, and containing much dark pigment. In 

 the upper part of each tegmentum is a round reddish grey centre, th& 

 nucleus of the tegmejitum, the red centre of Stilling, the superior olive 

 of Luys, lying near the side of the third ventricle. It is due to a 

 deposit of finely granular substance, containing branching pigmented 

 nerve-cells. 



Corpora quadrigemina. — In the centre of each grey matter is also 

 found, which is more abundant, although the cells are smaller, in the 

 posterior than in the anterior. In the former, the cells do not exceed 

 o-c^uoth of an inch diameter, but in the latter they are fewer, larger, 

 and more distinctly branched. The grey matter of the corpora quadri- 

 gemina is continuous in front with that of the optic thalamus, and behind 

 with that of the pons, and, by means of the nucleus of the roof of the 

 fourth ventricle, with the dentate nuclei of the cerebellum. 



Corpora geniculata. — Grey matter occurs in both. The inner con- 

 tains numerous small nerve-cells similar to those of the corpora quadri- 

 gcmina, mingled with fibres which pass through it from the same 

 source. Among them are also nuclei lying in clear spherical spaces. 

 The outer is densely filled with large yellow branching and fusiform 

 cells, and among them pass the fibres of the outer portion of the optic 

 tract, gathered in four or six lamiuiB, which alternate with thicker 

 layers of the cellular substance. 



The optic thalamus consists of grey matter which is mingled very 

 uniformly with the interlacing fibres of which it is in great measure 

 composed. The cells, most abundant in the anterior tubercle, are 

 large, stellate, and pigmented, about x^'ooth of an inch in diameter. 

 A large proportion of them are fusiform, with two processes, and there 

 are fewer small cells in the thalamus than in the other ganglia. 



The mkldle or gren commissure, connecting the two thalami, consists 



of small cells, densely massed together, and containing yellow pigment. 



The corpus striatum contains much grey matter, arranged in two 



chief masses. One of them, the intraventricular, is seen in the lateral 



