22 Journal of Comparative Neurology. 



inal branches do not however form perivascular plexuses; the 

 plexus formed by the sympathetic fibers seems quite indepen- 

 dent of them. The one set of fibers — vaso-motor or sensory — 

 is often stained to the exclusion of the other, the sensory 

 fibers staining more readily than the vaso-motor nerves. 



I have not been able to trace in its entirety the end-brush 

 of a single medullated nerve fiber terminating in the dura. In 

 a well stained preparation, the varicose terminal branches of 

 the sensory fibers are so interwoven that the ones coming from 

 a single medullated nerve fiber can not be separated from the 

 others. There would seem to be no doubt, however, that the 

 termination of the sensory fibers of the dura is an end-brush 

 spread over a relatively large area, the component parts of this 

 end-brush being very slender, varicose fibrils which terminate in 

 the connective tissue of the dura. 



As the preceding pages have shown, the writer has endeav- 

 ored to answer the question of the existence or non-existence 

 of vaso-motor nerves on the intracranial vessels, not by results 

 obtained in physiological experimentation, but rather from ob- 

 servations made by the aid of our modern histological methods 

 and the microscope. A knowledge of the existence of vaso- 

 motor nerves on the intra-cranial vessels must of necessity 

 weaken the position of physiologists, who, as a result of physio- 

 logical experimentation, no matter how carefully planned and 

 well executed such experiments may seem to be, deny the ex- 

 istence of such nerves. As the writer has conducted no physio- 

 logical experiments in the investigation, for the reason that he 

 has felt himself incapable of undertaking them, he deems it 

 presumptuous to discuss the results and conclusions of physiol- 

 ogists, who, from their observations, have gained the conviction 

 that the intra-cranial vessels were lacking in a vaso-motor nerve 

 supply. For a consideration of this phase of the question un- 

 der discussion I would refer the reader to the recent communi- 

 cation of Leonard Hill (lo), in which admirable work, he has 

 summarized his own numerous investigations in this field and 

 those of his co-workers and has given us a most critical digest 



