OF THE NERVOUS SYSTEM. 



371 



Fig. 120. 



tertiary, &c. A nerve, therefore, consists of a large bundle of ulti- 

 mate filaments, associated with each other in larger or smaller 

 packets, and bound together by the investing fibrous layers. When 

 a nerve is said to become branched or " divided" in any part of its 

 course, this division merely implies that some of its filaments leave 

 the bundles with which they were 

 previously associated, and pursue 

 a different direction. (Fig. 120.) 

 A nerve which originates, for ex- 

 ample, from the spinal cord in the 

 region of the neck, and runs down 

 the upper extremity, dividing and 

 subdividing, to be finally distri- 

 buted to the integument and mus- 

 cles of the hand, contains at its 

 point of origin all the filaments 

 into which it is afterward divided, 

 and which are merely separated 

 at successive points from the 

 main bundle. The ultimate fila- 

 ments, accordingly, are continu- 

 ous throughout, and do not them- 

 selves divide at any point between 

 their origin and their final distri- 

 bution. 



When a nerve, furthermore, is 

 said to " inosculate" with another 

 nerve, as when the infra-orbital 

 inosculates with the facial, or the 

 cervical nerves inosculate with 



each other, this means simply that some of the filaments composing 

 the first nervous bundle separate from it, and cross over to form a 

 part of the second, while some of those belonging to the second 

 cross over and join the first (Fig. 121) ; but the individual filaments 

 in each instance remain continuous and preserve their identity 

 throughout. This fact is of great physiological importance; since 

 the white or fibrous nerve-substance is everywhere simply an 

 organ of transmission. It serves to convey the nervous impulse in 

 various directions, from without inward, or from within outward ; 

 and as each nervous filament acts independently of the others, it 

 will convey an impression or a stimulus continuously from its 



Division of a NERVE, showing portion of 

 nervous trunk (a), aud the separation of its 

 filauieuts (b, c, d, e). 



