SYSTEMATIC SYNTHESIS OF TISSUES INTO ORGANS. 207 



282. THE OUTER TABLE is tough, and its edges very 

 irregular, and intermatched or even dovetailed. 



283. THE INNER TABLE is more brittle, and its edges 

 abut evenly by a harmonious joint. 



284. THE CONSTRUCTION OF THE CRANIUM IN THREE 

 TABLES of such different characteristics prevents blows 

 upon the head from jarring the brain, as the tables will 

 not vibrate in harmony, and hence they deaden or scat- 

 ter the effects. 



285. THE CRANIUM is COVERED with a thin, dense, 

 sinewy membrane, called PERICRANIUM. It adheres 

 closely to the bones, but outwardly its fibres become 

 continuous with the areolar texture of the head. 



286. THE CRANIUM is LINED with a thicker, dense, 

 sinewy membrane, called DURA-MATER. It 'adheres 

 closely to the bones, but on its inner surface, toward 

 the Brain, it is finished with a layer of basement mem- 

 brane, covered with a layer of serous cells, that keep 

 their surface constantly moistened with serum, and pre- 

 vent any friction as the brain moves against them. 



287. THUS THE CRANIUM is SEEN TO BE a dome- 

 shaped roof thrown over the Brain ; and if the latter 

 were removed the_ Cranium would remain an arched 

 vault of wonderful beauty, and having a perfect finish, 

 smooth and glairy, against which the delicate brain 

 might rest in safety. 



Fig. 160 represents a section of the head and neck upon the middle 

 line. 2, 3, 4, are the skull and its three tables. The membrane covering 

 the Cranium can be distinctly seen below 4, as it extends down joining the 

 lining at the edge of the hole in the base of the skull, from which it ex- 

 tends up, lining the cranium, and down, lining the spinal canal of the spi- 

 nal column or back bone, within which, 51, the spinal cord, cut off above, 

 is seen, not quite filling the canal. On the opposite side of the canal its 

 lining can again be traced and followed up within the Cranium till it 

 reaches around to the commencing point. 



Where the lining of the Cranium reaches its central line, near where 

 the section is made, it leaves the cranium and extends down quite to the 



282. Describe . 283. Describe . 284. What said of? 285. How ? 

 286. How ? 28T. What-? 



