SYSTEMATIC SYNTHESIS OF TISSUES INTO ORGANS. 291 



which forms a sinewy sheath to the millions of nervous 

 fibres it encloses. 



740. WITHIN THE SHEATH OF THE OPTIC NEEVE EX- 

 ISTS a very thin layer of pia mater, derived from that of 

 the Brain, and WITHIN THE PIA MATER ARE the true 

 nervous fibres, in bundles, having a small quantity of sin- 

 ewy tissue wrought around and between them. 



FIG. 197. 



741. THE NERVE (14, Fig. 197) EXTENDS FORWARD 

 an inch or more into the socket, where it "expands into 

 the form of the larger part of a sphere, nearly an inch 

 in diameter. 



742. THE SHEATH OF THE NERVE (15, Fig. 197) is 

 here thickened and made very dense by the addition of 

 sinewy fibres, and becomes (1, Fig.) the white or scle- 

 rotic (hard) coat of the eye, in the front part of which an 

 opening is left, through which the colored part of the 

 eye (6) shows. 



743. THE PIA MATER OF THE NERVE is also thickened 

 into (3, Fig. 197) an innumerable multitude of capillary 

 Blood-tubes, supported by a small number of sinewy 

 fibres, having in their meshes a large number of colored 

 cells, intensely black at the inner surface, where the 



740. What ? What does Fig. 197 represent ? 741. How does ? 742. What 

 does become ? 743. What does become ? 



