42 



MANUAL OF PHYSIOLOGY. 



The nerve or ganglion cells vary extremely in general form and 

 size. The commonest in the nerve centres are large bodies with 

 a clear well-defined single nucleus, and distinct uucleolus ; they 

 commonly have two or more processes, which are connected by 



FIG. 20. 



FIG. 20. Ganglion cells of frog, showing straight and spiral fibres. (After 

 Beale and Arnold.) 



FIG. 21. Cells from the sympathetic ganglion of a cat. The delicate 

 protoplasm has shrivelled here and there from the cell wall. 



nerve fibres to other cells, and to the axis-cylinder of nerve?. 

 This latter does not branch as the other processes sometimes do, 

 and when it can be traced, appears to enter the protoplasm, run- 

 ning towards the nucleus. 



The peripheral, nerve cells are generally much modified, and 

 often small compared with those in the centres. Besides the cells 

 in the sporadic ganglia, which are large rounded corpuscles with 

 but few processes there are many other bodies connected with 

 the peripheral nerves which cannot be called ganglion corpuscles. 

 They are, however, nevertheless nerve cells. 



Muscles or Contractile Tissues. When changes take 

 place in protoplasm adapting it specially for contraction, it is 

 termed muscle tissue. The large masses of this tissue attached to 

 the skeleton so as to move its various parts, form the flesh of the 



