HuBER, Innetvation of the Intracranial Vessels. 13 



obliquely, and are thus unlike the terminal branches of the vaso- 

 motor fibers which end in the muscular coat. These latter 

 course along in the intercellular cement between the muscle 

 cells and are parallel to them, that is, at right angles to the long 

 axis of the vessels. This difference — the mode of distribution 

 of the medullated nerve fibers and the vaso-motor is clearly seen 

 in methylen blue preparations of the pia-mater, in which both 

 sets of endings are stained on the same vessel. 



6. Where the entire ending of the medullated fibers is 

 made out, as in the preparation from which Fig. 2 was drawn, 

 the ending resembles the peripheral termination of sensory 

 nerves with free endings in other parts of the body, and is iden- 

 tical with the ending of sensory nerves found in the dura mater, 

 to be described later. I have therefore looked upon the med- 

 ullated nerve fibers found in the pia as sensory, since their 

 arrangement, size and mode of ending make it improbable that 

 they are the neuraxes of sympathetic neurons or of white rami 

 neurons. The term sensory nerve fibers is here used in the sense 

 commonly ascribed to it. Reference is had, to the dendrites of 

 neurons in the cerebral or spinal ganglia with T-shaped pro- 

 cesses. 



Vaso-motof nerves. On the vessels of the pia-mater, from 

 the larger vessels constituting the circle of Willis, to vessels 

 with a muscular coat of not more than two layers of involuntary 

 muscle cells, I have found perivascular nerves arranged in the 

 form of a plexus, which in every respect resemble the perivas- 

 cular nerves — vaso-motor nerves — found in the wall of vessels 

 in other parts of the body. They are non-medullated and 

 arranged in the form of plexuses which surround the vessels. 

 On the internal carotid artery, as soon as it leaves the carotid 

 canal, and on the vertebral after appearing in the spinal canal, 

 such perivascular plexuses are observed, and these may in suit- 

 able preparations be traced on to the anterior and middle cere- 

 bral and posterior communicating on the one hand, and basilar 

 and posterior cerebral on the other hand, and from the vessels of 

 the circle of Willis to the branches that arise therefrom. On the 



