lb Journal of Comparative Neurology. 



origin. So that relatively infrequently can they be traced to 

 medullated fibers, from which I believe they proceed. I 

 believe that these varicose fibers may be differentiated from 

 the vascular nerves which terminate in the non-striated 

 muscle tissue and which will be considered under the head of 

 vaso-motor nerves. As to the relation of the medullated nerves 

 and their endings to the vessels and their structural elements, 

 my observations are not so conclusive as to be entirely beyond 

 question, especially as concerns their ending. In methylen 

 blue stained preparations of the pia, mounted in ammonium 

 picrate-glycerine, especially if such preparations have been 

 mounted some days, in which case even relatively thick pieces 

 of tissue become quite transparent, it may be seen that the 

 larger and smaller bundles of medullated nerve fibers and the 

 majority of the single medullated fibers are situated in the con- 

 nective tissue adventitia of the vessels or in the neighboring 

 fibrous tissue. This is especially well shown, when, in the field 

 of observation, the nerves happen to lie by the side of the 

 artery. As is well known, non-striated muscle cells are readily 

 stained by methylen blue when applied to the fresh tissue. 

 Such cells retain their color after fixation. This fact makes it 

 easy to determine the relation of the medullated nerve fibers to 

 the muscular coat of the vessel. 



This relation holds good for the smaller as well as the 

 larger pial vessels. However, to make certain of this fact, 

 especial attention was paid to it, in a number of series of sec- 

 tions of pia containing vessels. The tissue was stained in 

 methylen blue, controlled under the microscope before fixing, 

 fixed in ammonium molybdate, hardened in alcohol, embedded 

 in paraffine and cut serially. The sections were then fixed to 

 slides and counter-stained in alum carmine. In cross or oblique 

 sections of vessels, in pial tissue thus prepared, the medullated 

 nerve fibers were found in the adventitia. It was however much 

 more difficult to reach a definite conclusion as to the disposition 

 of the terminal branches of these medullated fibers, and their 

 relation to the structure of the vessel wall. By studying sur- 

 face preparations of the pia, the conviction is gained that the 



