544 APPENDIX, 



On the Ganglionic Character of the Arachnoid Membrane. 



The following extracts contain the more important por- 

 tions of Mr. Rainey's observations " On the Ganglionic Cha- 

 racter of the Arachnoid Membrane of the Brain and Spinal 

 Marrow " * : 



" The first idea which suggested to me the resemblance of the arach- 

 noid to the sympathetic, was from the examination of a piece of the 

 former taken from the inferior and lateral part of the medulla oblongata, 

 when I observed, at the meeting of two of the chords situated between 

 the arachnoid and pia mater (called by Mengendie " Tussu Cellulo-vas- 

 culaire sub-Arachnoide "), a triangular body of the form and general 

 appearance of a ganglion, very similar to such as I had seen in small 

 animals. 



" This resemblance appeared more striking on observing a branch going 

 from the chord connected with this body, to the arachnoid membrane, 

 along which it ran for a considerable distance, dividing and sub-dividing 

 in its course, in the manner of a nerve ; the successive sub-divisions be- 

 coming more and more minute, and at the same time interlacing and 

 enclosing small areolse filled with corpuscular matter. These corpuscles 

 were so blended with the ultimate filaments of this chord as to render 

 indistinct their exact mode of termination. 



" Such was the connexion of one extremity of one of these chords. 

 The next point to be determined was the structure to which the other 

 extremity of the same chord had been attached. As, in this case, it had 

 been separated from its connexion, this could only be ascertained by 

 examining similar chords in other portions of membrane. This examin- 

 ation being made, I found that the end in question terminated either on 

 an artery or on a cerebro-spinal nerve. In the former case a chord, as 

 soon as it comes in contact with an artery, divides into branches which 

 ramify upon it, and run along its external coat, just as, to all appear- 

 ance, the branches of the solar plexus do on the small arteries supplying 

 the viscera in the abdomen. If the cerebral artery be rather large, and 

 situated between the arachnoid and pia mater, some of the branches 

 going from a chord form upon it a plexus, and others proceed on- 

 wards to the vessels of the pia mater. 



" In some instances a chord passes from an artery to the arachnoid 

 without dividing in its course, as just described ; but more frequently on 

 approaching the latter it sends off three or four large branches, which 

 pass to different parts of the membrane, and ramify in it, as before ex- 

 plained ; however, sometimes one of these branches either itself expands 

 into a large dense plexus, or joins other branches to form one, from 



* Medico-Chirurgical Transactions, 1846. 



