104 



TEXT-BOOK OF PHYSIOLOGY. 



different situations in accordance with peculiarities of function. 

 Though the nerve-cell and the nerve-fiber are but part of the same 

 neuron, it is convenient at present to describe them separately. 



The Nerve-cell. The nerve-cell, or body of the neuron, presents 

 a variety of shapes and sizes in different portions of the nervous 

 system. Originally ovoid in shape, it has acquired, in course of de- 

 velopment, peculiarities of form which are described as pyramidal, 

 stellate, pear-shaped, spindle-shaped, etc. The size of the cell 

 varies considerably, the smallest having a diameter of not more than 

 of an inch, the largest not more ikan ^^ ol iin men. Each ceil 



.. Neurilemma. 



FIG. 43. -A. Efferent neuron. 



. 



Terminal 

 branches. 



consists of granular; striated protoplasm, containing a distinct ves- 

 icular nucleus and a well-defined nucleolus. A cell memJbja^p ha^ 

 not been ofrfifirverL From the surface of the adult cell portions of 

 the protoplasm are projected in various directions, which portions, 

 rapidly dividing and subdividing, form a series of branches, termed 

 dendrites or dendrons. In some situations the ultimate branches of 

 the dendrites present short lateral processes, known as lateral buds, 

 or gemmules, which impart to the branches a feathery appearance. 

 This characteristic is common to the, cells of the cortex of the cere- 

 brum and of the cerebellum. The ultimate brariclfe of the den- 



