582 THE POSTERIOR PITUITARY AND THE NERVOUS SYSTEM. 



We are now able to say that they are, for the neuroglia- fibrils 

 of the substance of the brain and cord represent their blood-supply, 

 just as the cellular capillary net-work of any other organ represents 

 its blood-supply. 



Indeed, we must not overlook the fact that, while the 

 neuroglia-fibrils representing the capillary supply of the cere- 

 bro-spinal substance are not supplied with vasomotor nerves, 

 the peripheral vessels connected with the organ are, thus fur- 

 nishing it with what we have termed elsewhere an extrinsic 

 supply. This extrinsic system would thus be represented by 

 the pial vessels, which, as shown by Andriezen, 66 are supplied 

 with vasomotor nerves. "We find," writes this investigator, 

 "that it is possible to stain the vasomotor nerves with Golgi's 

 method. Starting from the carotid and vertebral plexuses we 

 can trace them no farther than the circle of Willis by anatom- 

 ical dissection (using a lens). Do nerves accompany the cere- 

 bral arteries as they go off from the circle of Willis; and, if 

 so, how far; and what is their ultimate distribution? Our 

 observations on the kitten's brain show that bundles of nerve- 

 fibers accompany the middle cerebral artery (the one specially 

 chosen for our study) and its branches in the pia. These fibers 

 run in tortuous and zigzag fashion, and in the finer pial 

 branches they can be seen to form a very fine (non-anastomotic) 

 plexus of fibrils lying between the outer and the muscular coats. 

 From this perimuscular plexus terminal fibrils issue which, run- 

 ning a short distance along the muscular layer either longi- 

 tudinally, transversely, or obliquely, end in small spherules: 

 little ovoid bulb-like arrangements abutting against the mus- 

 cular elements (cells). We have succeeded in tracing these 

 terminals and their distribution to the finest pial cells, but no 

 farther. The intracortical continuations of the pial vessels 

 have constantly failed to give us the least evidence of this 

 perimuscular plexus, which therefore so far as our investiga- 

 tions go we are compelled at present to imagine as stopping 

 with the pial branches, and not continued along the intracortical 

 vascular branches." 57 This evidence, added to the facts already 

 outlined concerning the pericerebral vascular supply, seems to 



"Andriezen: Brain, Winter, 1894. 



57 The word "not" is alone italicized by Dr. Andriezen. 



