THE CENTRAL NERVOUS SYSTEM. 



313 



FIG. 342. 



idal elements, which become more widely separated and of greater 

 size on approaching the deeper parts of the zone ; in this situation 

 their basal diameter may reach 4050 p.. 

 The pyramidal cells, in addition to 

 the general outlines of their bodies, 

 are distinguished by the arrange- 

 ment of their processes ; the pro- 

 toplasmic ramifications are disposed 

 as the principal apical processes, 

 which extend towards the periphery 

 as far as the sub-pial zone (Retzius) 

 and by repeated division form a rich 

 arborization within the outer layers 

 of the cortex, and as lateral basal 

 processes, which pass obliquely from 

 the base and break up into rich net- 

 works of delicate terminal protoplas- 

 mic threads ; in addition, numerous 

 smaller lateral processes are given 

 off from the sides of the cell. Not- 

 withstanding the profusion of the 

 fibrils resulting from the subdivision 

 of the protoplasmic processes of these 

 cells, it is highly probable that the 

 fibrils terminate without uniting 

 with one another. From the blunt, 

 central end of the cell the axis-cyl- 

 inder process extends into the white 

 matter, where it becomes continuous 

 with a nerve-fibre. These axis-cyl- 

 inder prolongations give off recurrent 

 collateral processes, which bend 

 towards the periphery. The pyrami- 

 dal body of the cell contains a large 

 round or oval nucleus, with a dis- 

 tinct nucleolus, embedded within a 

 finely granular protoplasm, masses of 

 brownish pigment almost always occupying the base of the cell. 

 The larger pyramidal cells are surrounded by pericellular lymph- 

 spaces, which probably communicate with the extensions of the 

 subarachnoidean space continued with the prolongations of the 

 pia accompanying the blood-vessels within the cerebral tissue. 



4. The fourth layer embraces a closely-packed zone (.3-. 4 mm.) 

 composed of small, irregular, oval or angular nerve-cells, 7- 



Section oi cerebral cortex (motor area) 

 of child stained by Golgi's silver method: 

 A, layer of neuroglia-cells ; B, layer of 

 small pyramidal ganglion-cells ; C, layer 

 of large pyramidal cells ; D, layer of ir- 

 regular smaller cells. 



