826 



THE CENTRAL NERVOUS SYSTEM 



telodendrions of the posterior root-fibres through the dendrites of the 

 anterior horn cells towards their cell-bodies, but not in the opposite 



Fig. 323. a e shows the development of the pyramidal nerve-cells of the cerebral 

 cortex in a typical mammal; a, neuroblast with commencing axon; 6, dendrites 

 appearing; d, commencing collaterals. A D shows the different degree of com- 

 plexity in the fully-developed pyramidal cells in different vertebrates: A, frog; 

 B, lizard; C, rat; D, man (Donaldson, after Ram6n y Cajal). 



direction, and in general the direction of conduction is from the den- 

 drites towards the cell-body. 



Some investigators believe that the fibrils already spoken of as 

 forming a felt-work in the protoplasm of the nerve-cell may run right 



Fig. 324. Cells from the Gasserian Ganglion of a Developing Guinea-Pig. The 

 originally bipolar cells are seen changing into cells apparently unipolar. The 

 same process occurs in the cells of the spinal ganglia (Van Gehuchten). 



through from one cell to another, thus constituting an actual anatomical 

 connection between the neurons, and that such a connection may be 

 established also by fibrils which do not enter the cells at all, but run in 

 the intercellular substance of the grey matter. Such a continuity of 



