142 OF THE PI) NOTIONS OF 



dissimilar from this oscillatory motion, that on the 

 same supposition he very ingeniously explains, prin- 

 cipally by means of the vapour of the ventricles (called 

 by him the denser ether),* first, the association of ideas, 

 and again, by the assistance of this, most of the func- 

 tions of the animal faculties. (I) 



NOTES. 



(A) The Pia Mater and Tunica Arachneides were considered 

 as the same, till the Anatomical Society of Amsterdam con- 

 firmed, in 1665, the doubts which were arising on the subject 

 and Van Home demonstrated both membranes distinctly to his 

 pupils. The Dura Mater corresponds with the fibrous mem- 

 wanes, the Pia Mater with the cellular, and the Tunica Arach- 

 noides with the serous. The latter is, in nature, office, and dis- 

 eases, exactly like the serous ; — a close sac, affording, as the 

 peritonaeum does to the abdominal viscera, a double covering to 

 Hie brain and spinal marrow and the nerves before their departure 

 through the foramina of the Dura Mater, and lining the ven- 

 tricles ; insulating the organs on which it lies, and affording 

 them great facility of movement ; and liable to all the morbid 

 affections of serous membranes. f 



(B) Fibres are very evident in the cerebral substance. Mr. Baner 

 has discovered globules, but then he finds fibres to be series «f 

 globules. ~l 



* Er. Darwin has carried these opinions of Hartley «till farther, Zoom*- 

 mia. T. 1. 



t Bichat, Traite de* Membranes. 

 X Phil. Trmm. IMS. 



