THE STRUCTURE OF THE CEREBRUM. 167 



in which is the gray corpus striatum. A thin envelope of gray 

 substance, called the cortex, forms the surface of the hemisphere. 

 The entire cerebral substance, both the white and the gray, is 

 composed of neurones and sustentacular tissue, the latter being 

 made up of neuroglia, ependyma and mesoblastic connective 

 tissue. Of necessity the cerebrum possesses a rich blood supply. 



The Neurone (Fig. 49). The essential element in the nervous 

 system is the neurone. The neurone comprises the cell-body, 

 its processes and end-organs. The cell-body, perikaryon, or 

 neurone center, is a granular reticulated mass of protoplasm of 

 variable form. It ranges in man between four microns and one 

 hundred and thirty- five microns in diameter. The size of the 

 cell-body is usually proportionate to the length of the processes. 

 Its shape, which is spherical, fusiform, pyramidal, stellate or polyg- 

 onal, is dependent upon the number and mode of origin of its 

 processes. The cell-body has a large vesicular nucleus in which 

 there are one or more nucleoli. It also possesses a centrosome in 

 spinal and sympathetic ganglia. Its reticulated appearance is 

 due to a net-work of fine fibrilla which form a close net about the 

 nucleus. These nbrillae may be seen in all parts of the cell-body 

 and they are continued into the processes given off from it. Masses 

 of deeply staining material, called tigroid bodies or Nissl bodies, 

 produce the granulated aspect of the perikaryon. The tigroid 

 bodies are found in the receptive side of the neurone, viz., in the 

 dendrites and throughout the cell-body, except in the axone- 

 hillock (Fig. 50). 



The processes of the neurone are from one to eight or a doezn 

 in number and are of two kinds, namely, the dendrites and the 

 axones. Dendrites, like the cell-body, are protoplasmic in com- 

 position and of irregular contour, except in sensory nerves, where 

 they are smooth, like axones. In all cases they contain fibrillae 

 prolonged from the cell-body. They branch richly and end 

 in beaded points. The terminal branches are called telodendria. 

 Dendrites may form synapses with axones of other neurones, 

 may terminate in special end-organs, or end free among the cells 

 of any tissue. They are developed later than the axones and 

 are not always present. An active cell usually has several den- 



