264 The Older Doctrines [lect. 



also within their cavities, delicate threads, forming a sort of 

 marrow, and these threads by centripetal action determine the 

 outflow of the spirits from the gland and from the ventricles 

 into the nerves. 



" You see also that in each of these little tubes there is a 

 "sort of marrow composed of a large number of exceedingly 

 "delicate threads starting from the proper substance of the 

 " brain." (He explains elsewhere that the proper substance of 

 the brain forming the walls of the ventricles is composed of an 

 intricate network of these delicate threads, the meshes of the 

 network being the pores or mouths of the tubular nerves.) 

 " The ends of these threads terminate on the one hand at the 

 "internal surface of the brain looking towards the ventricles, 

 " and on the other hand in the skin or other tissues in which 

 " the tubes which hold them end. But, since this marrow does 

 " not serve for the movement of the members " (is not motor in 

 function as we should say but sensitive only), " it will be enough 

 " at the present moment if you know that it does not wholly 

 "fill the tube which holds it so that the animal spirits have 

 " ample room to flow readily from the brain to the muscles to 

 " which these little tubes, which ought here to be considered as 

 " so many little nerves, are distributed. 



***** 



" Know then that a very large number of little threads like 

 "the above begin to separate all of them, the one from the 

 "other, at the internal surface of the brain where they take 

 " their origin, and spreading thence over all the rest of the body 

 " serve as organs of sense. 



***** 



"In order to understand how the brain can be excited by 

 " external objects which affect the organs of sense, so that all 

 "the members can be moved in a thousaud different ways, 

 "imagine that the delicate threads, which as I have already 

 " said arise from the inside of the brain and form the marrow 

 " of the nerves, are so disposed in all those parts which serve as 

 " the organs of any sense that they can easily be set in motion 

 " by the objects of the senses, and that, whenever they are thus set 

 " in motion, even ever so little, they, at the same instant, pull 



