78 



NERVOUS SYSTEM OF VERTEBRATES. 



from one of the dendrites at some distance from the cell-body. 

 Figure 39 shows several forms of nerve cells with reference to 

 polar differentiation. 



With respect to the form and disposition of their neurites, 

 two chief types of nerve cells are distinguished. In the first and 

 more common type (type I) the neurite is long and serves to make 

 a connection with some distant nerve cell, muscle cell, gland cell, 

 etc. In the second type (type II) the neurite is short and divides 



Fig. 39. — Several types of nerve cells from the central and peripheral nervous 

 system of vertebrates. A, spinal ganglion cells; B, a Purkinje cell from the brain 

 of the sturgeon; C, a cell from the nucleus praeopticus; D, a granule from the 

 cerebellum; E, a cell of type II from the tectum opticum. 



into terminal branches in the near vicinity of its cell, serving to 

 make connection with several other cells of the same nerve center 

 (Fig. 39, E). 



The structural differentiation of the cell is correlated mth a 

 functional polarity. For, the nerve impulse witliin a given cell, 

 whatever its source, begins in the dendrites or cell-body and is 

 transmitted toward and along the neurite until it is passed on to 

 some other cell through the branches of the neurite. In the case 



