126 O. LARSELL 
slender varicosed fibers which in turn subdivide. These appar- 
ently correspond to the fibers observed and figured by Karsner 
(11) in the pulmonary artery of the dog. The final fibers pass 
between the smooth muscle bands of the tunica media of the 
arterial wall, and give off twigs which terminate in relation. to 
the smooth muscle cells, as above described and as illustrated 
in figure 15, which represents a portion of the wall of an arteriole. 
Fig. 13 Distribution of nerve fibers in the muscular portion of the wall of 
the pulmonary artery within the lung. Rabbit R38. Methylene-blue stain. 50z. 
Camera lucida. X 75. 
Nerve fibers are present in the walls not only of the larger 
vessels, such as represented in figure 13, but also in the various 
subdivisions of the pulmonary arterial system, including the 
arterioles. This may be seen by examination of figure 14, which 
represents several orders of branches of a pulmonary vessel, as 
shown in a single section. That the blood-vessel is a branch of 
the pulmonary artery can be judged from its relation to the 
bronchus which is also shown in the figure. W. 5S. Miller has 
