498 ELEMENTARY PHYSIOLO(JY lkss. 



which they are seen, but speaking broadly and generally 

 they may be said to resemble in their most obvious 

 features the motor cells of the spinal cord, whose struc- 

 ture we have previously desci'ibed (p. 407). Like the 

 latter, each nerve cell of a sympathetic ganglion contains 

 a large and conspicuous nucleus, and the cell body is pro- 

 longed into a varying but usually large number of 

 branching processes (dendrites). Moreover, eai^h cell 

 possesses one process which does not branch but passes 

 away from the body of the cell as a (usually) non- 

 medullated nerve fibre, to be distributed to the various 

 tissues (p. 495) which it influences, and is in this respect 

 similar to the axis-cylinder process of a cell of the spinal 

 cord. Each ganglion is also connected with nerve fibres 

 which come to it from the central nervous system (Fig. 

 157). These fibres mostly end in connections with the 

 nerve cells. Sometimes a fibre does not end in the first 

 ganglion it meets, but passes right through it into one 

 of the nerves going off from that ganglion, and so reaches 

 some other more distant ganglion. The number of 

 nerve fibres which thus pass into the ganglion from the 

 spinal cord is much less than the number of nerve cells 

 in the ganglion ; hence many more nerve fibres are found 

 coming, from the ganglion than entering it. By this 

 arrangement each ganglion provides, as it were, a sort of 

 junction by means of which any nervous impulses which 

 reach it along any one path may be the more readily and 

 widely distriljuted, along several paths, to the tissues. 



10. The Structural Arrangements of the Brain and 

 Spinal Bulb (Medulla Oblongata).— The brain is a very 

 complex organ consisting of many parts. It occupies the 

 cavity of the skull and is thus placed at the upper end of 

 the spinal cord with which it becomes connected by means 

 of the spinal bulb ' ; this passes insensibly into, and in its 

 lower part has the same structure as, the sjjinal cord. 

 When viewed from the side, after the removal of the parts 



1 Throughout this section we shall use the word "bulb" in shortness 

 for spinal bulb, and instead of the older name " medulla oblongata." 



