THE NERVES. Ill 



But nerves arising from different tracts may be enclosed 

 in the same bundle, and this may consequently have 

 different endowments. Hence the distinction into simple 

 and compound nerves. Those filaments coming from the 

 same tract are called Funiculi, and form simple nerves. 

 Those coming from different tracts are called Fasciculi, 

 and form the compound nerves. The ninth is a simple, the 

 spinal are compound nerves. 



The course of the nerve fibres is straight, and without 

 branches, from their origin to their termination. 



A communication of nerves by means of their funiculi and 

 fasciculi, forms a kind of net work called Plexus; the 

 nerves, however, do not run into each other and form an 

 anastomosis after the manner of blood vesse.ls ; they simply 

 come together, enter each other's sheaths, run side by side, 

 but are not fused into one. 



The use of a plexus is two-fold. 1st. It intermixes fibres 

 of fundamentally different endowments, as the spinal ac- 

 cessory and par vagum the former a motor, the latter a 

 nerve of sensation. 2d. It advantageously distributes nerves 

 of the same endowments, as in the Brachial plexus, where 

 the filaments of five segments of the spinal cord are 

 mixed together, and proceed in this mixed state to the 

 several parts upon which they are distributed. By which 

 arrangement no part can be paralyzed, till all the five 

 segments or centres of action are destroyed while if each 

 centre sent its nerves singly and alone to any part, when 

 that centre becomes destroyed, the part upon which its 

 nerves are spent will inevitably suffer paralysis. 



The nerves terminate (Fig. 13) in loops or arches, or 

 more properly speaking, they have no free extremity, but 

 form circles; those, for instance, going from the spinal 

 marrow and brain to the circumference of the body, which 

 conduct the motor power, and called efferent while the 

 afferent, which begin where the others stop, are contin- 

 ued back again to the place from whence they started 

 thus completing the circle, and conducting to the central 

 nervous ganglia, sensory impressions. 



