ON THE NERVES IN GENERAL. 491 



tween different nerves, rarely between the nerves of one side 

 and those of the opposite. 



It is especially in the nervous arches that the junction of the 

 filaments is the most evident: the most remarkable of these 

 arches is that which results from the union of the par vagum/of 

 the right side and of the solar plexus, and which Wrisberg has 

 described under the name of ansa communicans memora- 

 biles. 



A plexus is only multiplied anastomoses. Scarpa* has giv- 

 en a very good description of them; but he is wrong in assi- 

 milating them to the ganglions. The manner in which the 

 four last cervical pairs unite with each other, and with the 

 first dorsal, to form the brachial plexus, furnishes a remarka- 

 ble example. The cervical, lumbar, sciatic, plexuses, &c. are 

 also examples in point. These plexuses are so disposed that the 

 nerves which arise from them derive ttyeir origin at once, for 

 the greater part at least, from a certain number of the nerves 

 which constitute them. 



Bichat admits that there is in plexuses something besides a 

 simple intimate mixture of the nerves. Munro says that they 

 contain gray substance, and may be considered a new origin 

 of the nerves which depart from them; but this is by no means 

 demonstrated. 



The ganglions consist of tumours which contain, besides 

 the nervous filaments, a substance which is foreign to them; 

 the nervous filaments which are there mingled are much finer; 

 they present, consequently, a greater complication than the 

 two other modes of communication. They will be examined 

 after the nerves, from which they differ in several characters. 



776. The termination of the nerves takes place after they 

 have traversed the anastomoses, the plexuses, or the gangli- 

 ons, or directly without their being interrupted from their ori- 

 gin. The manner of their termination is rather obscure. 

 They are seen only to be deprived of their neurilema towards 

 their latter extremity, and to become in consequence very soft; 

 so that it is then very difficult to trace them. They swell in 



* Anat. annot. de gangliis etplexubus. 



