HuBER, Innefvation of the Intracranial Vessels. 2 1 



The peri-vascular plexus on the middle meningeal has been 

 observed on this vessel as soon as it reaches the dura, and I 

 have been able to trace it along its course until the arterial 

 branches were reached having a musculature consisting of two 

 layers of involuntary cells. My reason for believing the non- 

 medullated nerves, which form this peri-vascular plexus, to be 

 neuraxes of sympathetic neurons, is the fact that in some of the 

 best stained preparations, fine nerve fibrils, coming off from the 

 perivascular plexus, could be traced into the muscular coat of 

 the vessels, where such fine nerve fibrils assumed a course paral- 

 lel to the long axis of the involuntary muscle cells of the vessel 

 wall, between which they seemed to terminate. For such a 

 perivascular plexus see Fig. 5. 



The medullated nerves of the dura which, with other ob- 

 servers, I regard as sensory, comprise the two kinds of nerves 

 described by Alexander. Bundles of medullated nerves accom- 

 panying the arteries are readily stained in methylen blue; two 

 such bundles are shown in Fig. 5. In portions of the dura free 

 from larger vessels, are found bundles of medullated nerves 

 (see Fig. 6) having a course quite independent of the vessels ; 

 these I take to be the dural nerves described by Alexander. In 

 their mode of ending I find no difference between the medul- 

 lated nerves of the dura accompanying the vessels and those 

 having a course independent of them. In each case the medul- 

 lated nerves, after branching here and there at the nodes of 

 Ranvier, lose their myelin and continue as non-meduUated fibers. 

 These non-medullated fibers after further branching, terminate 

 in long varicose fibrils, which may now and then be traced 

 through several fields of the microscope when the preparation 

 is viewed under a magnification of about 400 diameters. 



These non-medullated terminal branches interlace in every 

 possible manner, as may be seen in Fig. 6, giving an appear- 

 ance which is commonly termed a nerve plexus; the identity of 

 the nerve fibrils is, however, not lost in this "plexus" as one 

 meets with no anastomoses of the nerve fibrils. The medullated 

 fibers accompanying the arteries of the dura often terminate 

 over them or in such a way as to surround the vessels; their term- 



