THE CEREBRUM, AND ITS FUNCTIONS. 689 



The fourth layer contains broader and more regularly arranged groups of 

 cells and nuclei, which together with the bundles of fibres between them 

 present a distinctly faulike arrangement. The fifth layer is pale, with a 

 similar structure, but with the fanlike appearance less distinct. The x/'.r//i 

 layer is reddish-gray, and contains similar cells to those above described 

 with others that are rather larger. The elongated groups of cells are fewer 

 ill number. Its deep surface blends with the central white axis of the con- 

 volution, into which its cells are scattered for some distance. The seventh 

 layer is the central white stem or axis of the convolution, which gives off oil 

 every side bundles of fibres that radiate outwards, becoming exceedingly fine 

 as they reach the surface, in consequence of some of the fibres terminating 

 in the cells of the different layers, whilst others bend round and run hori- 

 zontally, either crossing the convolution transversely, or running longitudi- 

 nally in the same direction. Besides these fibres which form the central white 

 axis of the convolution, another set springing from the same source converge 

 or rather curve inwards from opposite sides to form arches along some of the 

 gray layers. They appear to be partly continuous with those of the radiating 

 or divergent set which bend round to follow a similar course. All these fibres 

 establish an infinite number of communications in every direction, between 

 different parts of each convolution, between different convolutions, and be- 

 tween these and the central white substance. In other central convolutions 

 situated more anteriorly the layers are less pronounced, and instead of all the 

 cells of the several layers being small, a certain proportion of much larger 

 cells are found chiefly occupying the two internal layers. These cells are 

 pyramidal, with quadrangular bases directed towards the central white sub- 

 stance, and each gives off four or more processes which run partly towards 

 the central white axis, and partly parallel with the surface of the convolu- 

 tion to be continuous with arciform fibres. The processes frequently sub- 

 divide into minute branches, which form part of the network between them. 

 The apical extremity runs straight outwards, and gives off minute branches 

 which are lost like the process itself in the surrounding network. Slight 

 modifications occur in the vesicular structure of other convolutions. It is 

 interesting to note that Mr. Clarke was unable to perceive any difference 

 whatever between the cells of the convolutions in Man and those of the ape 

 tribe. 



Professor Meynert, in an elaborate essay, has recently given an anatomical descrip- 

 tion of the brain, of which the following is an outline. Many points, however, are 

 here unavoidably omitted, especially those relating to the structure of the medulla 

 oblongata and pons, for which the reader is referred to the original article contained 

 in the second volume of Strieker's Manual of Histology, translated for the Sydenham 

 Society. 



Professor Meynert points out that the peripheric nerves of the body collectively 

 converge towards the gray matter of the cerebral cavities, spinal cord, and medulla 

 oblongata, and that after passing through these with more or less interruption or 

 segmentation in the ganglion cells, they diverge to terminate in the great expansion 

 of gray >ub>tanee which forms the cortex of the cerebral hemispheres. The entire 

 collection of fibres he terms the " Projection system," and commences its descrip- 

 tion not with the peripheric nerves, hut from the hemispheres of the cerebrum 

 and cerebellum. He divides it into three links, with three masses of gray matter. 

 The first mass of gray matter is the cortex of the cerebrum and cerebellum (CCH 

 and C'f), Fig. 244), and the first link of the projection system is represented essen- 

 tially by the corona radiata (CR), which consists of fibres extending from the cerebral 

 cortex to the ganglionic masses of the corpus striatum and optic thalamus (LN, CN, 

 OT), which constitute the second mass of gray matter. The second link of the pro- 

 jection system is composed of fibres that extend from those ganglia to the gray sub- 

 stance around the central cavities, which is the third gray mass, and is represented 

 by the system of thecrus cerebri. The third link is formed by the nerves which arise 

 from the above-named gray substance of the central cavities, beginning with the 



