SYSTEMATIC SYNTHESIS OF TISSUES INTO ORGANS. 269 



Cranial Ganglia. 



634. IF THE UPPER PART OF THE SKULL AND ITS UN- 

 ING BE CUT THROUGH AND LIFTED FROM THEIR PLACES, the 



brains will be presented to view, standing up, a jelly-like, 

 tremulous mass, with a surface perfectly smooth, glairy, 

 and well fitted to the portion of skull removed. (See 

 Figs. 45 and 46.) 



635. AN EXAMINATION WILL DETERMINE that the 



surface under view is an exquisitely beautiful specimen 

 of secretory tissue, composed of a single layer of thin, 

 scale-shaped, but not dry cells, upon a basement mem- 

 brane supported by a mere shadow, so delicate is it, of 

 sinewy fibres. 



636. This SPIDER'S WEB MEMBRANE (ARACHNOID) 

 extends over the general surface of the brains, without 

 following its smaller indentations, passing across from 

 point to point, being parallel to the inner surface of the 

 lining of the skull, with which in life it is in contact. At 

 the indentations of the brain the end of a small tube can 

 be adroitly inserted, beneath, and air blown under it, 

 raising it up and bringing it into view very beautifully. 



637. Remark. THE OUTER SURFACE OF THE BRAIN AND THE INNER 

 SURFACE OF THE LINING OF THE SKULL are precisely alike, and at various 

 points will be found to be continuous ; and the idea is usually expressed 

 by saying the covering of the brain is reflected on the lining of the 

 skull, or the inner layer of the lining of the skull is reflected over the 

 brain. 



638. WHEN THE ARACHNOID is REMOVED, the surface 

 below is found to be very uneven, corrugated, or convo- 

 luted, like the surface of a peach-stone, the eminences 

 being called convolutions, and the indentations being 

 called anfractuosities. Near the surface THE ANFRACTU- 

 OSITIES ARE GROOVES, but a little deeper their sides 

 touch, as represented in the Figs. 



639. THE SURFACE OF THE CONVOLUTIONS AND AN- 



634. What ? 635. What will ? Name of membrane? 636. How does 

 extend? 637. What said ? 638. What seen ? Where are ? 639. What is 



