566 THE POSTERIOR PITUITARY AND THE NERVOUS SYSTEM. 



rilemma. Indeed, the similarity even extends to the subdivision 

 of the dendritic central canal into fibrils, for Berdal says, re- 

 ferring to the dendrites: "These prolongations seem striated 

 longitudinally as is the cell, and appear to be composed of 

 fascicles of fibrils which are continuous with those of the cellu- 

 lar body." A single structure is missing, however, that which, 

 we have just seen, is represented by the neuroglia in cerebro- 

 spinal nervous elements: i.e., the neurilemma. Obviously, the 

 absence of a protective insulating sheath around the cell-body 

 of the neuron and its extensions, considering their functional 

 importance as generators of nervous energy, becomes absolutely 

 incompatible with existing conditions, since the myelin would 

 thus be exposed externally. Indeed, that the cell-body and its 

 dendrites are supplied with an external sheath is shown by the 

 following lines of Berkley's 63 : "Around the body of the cell 

 we find an insulating mass of fluid contained in the pericellular 

 lymph-sac, and as a capsule to the sac there appears a slight 

 condensation of the tissue at this point that would take the 

 place of a retaining membrane. This membrane apparently 

 terminates where the first of the gemmulae are thrown off from 

 the ascending portion of the primordial process, and likewise 

 at the location where the first buds appear on the basal den- 

 drites. Does the insulating fluid and covering really end at 

 this point? In absolute-alcohol sections of the cortex of the 

 cerebellum taken parallel with the surface and stained with 

 the anilines, particularly the blue-black, it is quite readily 

 demonstrable that the thin membrane, which is now undoubt- 

 edly composed of fine glia- filaments, does not really cease at this 

 point, but becomes attenuated, and continues to ascend and 

 cover the protoplasmic prolongations of the cell." This speaks 

 for itself; the cell-body of the neuron and its dendrites are supplied 

 with a covering which is to them what the neurilemma is to nerve- 

 fibers; this covering is similar to that investing these nerve- fibers: 

 i.e., a sheath of neuroglia. 



This only affords, however, information concerning the 

 neuroglia supplied to the neuron per se, and to the structures 

 which the axons become a short distance below the cell: i.e., 



"Berkley: Loc. cit., pages 90 and 91. 



