94 DARMON A. RHINEHART 



leaving the main trunk. They extend for a longer or shorter 

 distance around the vessels, divide again and again, and finally 

 become resolved into an intricate network of fine end fibrillae. 

 This elaborate nervous plexus is located in the perivascular 

 connective tissue and in the tunica adventitia of the arterial walls, 

 while some of the finer fibrillae penetrate into the tunica media. 



The larger nerves are composed of bundles of axis-cylinders, 

 and the branching of these consists merely in some of these axis- 

 cylinders leaving the main bundle and taking a different direc- 

 tion. As this method of branching continues the axis-cylinders 

 finally come to lie singly. From these single fibers are given off 

 true branches, which do not decrease in size but are usually more 

 irregular, more varicosed, and have a more wavy course. The 

 final end fibrillae are often very short, are beset with many vari- 

 cosities, and soon end in irregular enlargements or end-knobs. 



The many crossings and recrossings of the nerves, together with 

 their elaborate branching, is very misleading, and often gives the 

 appearance, especially under low magnification, of true anasto- 

 moses. In the thicker sections where the nerves are great in 

 number it is often impossible to distinguish the separate fibers. 

 But if relatively thin sections are examined under high magni- 

 fication the fibers can all be traced individually. Therefore, 

 contrary to the statement of Berkekey, true anastomoses do not 

 occur. In examining these nerves it is seen that the origin and 

 ending of the most of the branches cannot be traced in a single 

 section for they are only fragments, the remainder having been 

 cut away. 



All the nerves that go to make up the perivascular plexuses are 

 more or less varicosed. Even the axis-cylinders that form the 

 large nerve bundles are beset with many irregular enlargements. 

 There may also be precipitations of chrome-silver between the 

 axis-cylinders in places, so as to give the nerves the appearance 

 of solid cords. At the points of branching of all the nerves there 

 are irregular, triangular, black masses, which may be either a 

 portion of the nervous structure or a black precipitate. The 

 smaller nerves, where the axis-cylinders lie singly, are more vari- 

 cosed than the corresponding parts of the larger nerves; this 



