256 The Older Doctrines [lect. 



" destitute, at least in health, any of the parts on which they 

 " bestow their products, although they do not always supply 

 "them either in the same quantity or the same quality. 

 " Nerves therefore serve the same purpose to the brain that the 

 " great artery does to the heart, and the vena cava to the liver, 

 "in as much as they convey to the instruments to which it 

 " ought to be sent the spirit prepared by the brain, and hence 

 "may be regarded as the busy attendants and messengers of 

 " the brain. 



" The material, however, for the animal spirit, is supplied by 

 " the vital spirit, abounding as this does in the arteries which 

 " in numerous series reach both the hard and the thin membrane 

 " (dura mater and arachnoid) investing the brain, as also by 

 " the air which in breathing is drawn in towards the brain, 

 " on the one hand through the minute holes drilled in the sixth 

 " (or ethmoid) bone of the skull for the special purpose of smell, 

 "and on the other hand through those orifices in the skull which 

 " look towards the palate, as we explained very early in this work. 

 " And indeed air where it can find an entrance makes its way 

 "into the right and left ventricles of the brain, and into the 

 " one which lies between these. This vital spirit, although we 

 " may regard it as being very abundant in all the vessels and 

 "sinuses of the membranes of the brain is however chiefly 

 " brought into the right and left ventricles of the brain by the 

 " larger branches of the arteries which are directed to the sides 

 " of the gland receiving the mucus of the brain (the pituitary 

 "gland); offsets from these imbedded in processes of the thin 

 " membrane enter the lower parts of the right and left ventricle 

 "and then make their way over their whole extent. But 

 " besides these arteries a particular vessel from the fourth sinus 

 " of the membrana dura, passing under the body which resembles 

 " in shape a turtle or a chamber built in the form of an arch, 

 "reaches the front part of the brain by the cavity which is 

 " common to the right and left ventricles. This after several 

 " flexures divides at length into two parts, one of which passes 

 " to the right and the other to the left ventricle, and so joins 

 "the arteries of that situation, forming a net which resembles 

 "the membranes of the foetus more than anything else. 



