233 



tions of the radiating and circular fibres regulating the size 

 of the pupil. 



The strong fibrous tissue of the choroid and its appendages 

 seems to be distributed, wherever it is required, beneath the 

 delicate investing membrane, to use a familiar illustration, 

 like tbe padding of a coat. Thus, it is to be found in the 

 iris, surrounding its vessels, on the external and internal 

 surface of the ciliary circle, in the tissue constituting the 

 tapetum lucidum of the lower animals, and it is not absent, 

 though it has not the brilliancy, in the same situation in 

 man himself. 



The ciliary processes are intimately adherent to the zonule 

 of Zin, Avith an intervening pigmentary coating, the various 

 little folds and corrugations of the one being received into 

 corresponding recesses and depressions in the other. When 

 the processes are forcibly severed from their attachment the 

 pigment-cells appear, at least in many places, to be torn, as 

 it were, into two layers, thus liberating the contained pig- 

 ment-granules so as to stain the surrounding parts. Under 

 a low power the general appearance of the ciliary circle is 

 not unlike a beautiful though minute model of a mountainous 

 country, and in the physiology of adaptation the little spurs 

 and folds, taldng a circular or transverse direction, play as 

 important a part as the principal mountain chains, for thereby 

 any tendency to dislocation is obviated when pressure is being 

 exerted upon the fluid in the canal of Petit, and through this 

 upon the free margin of the lens. Wiiether the old doctrine 

 of the splitting of the hyaloid membrane at the outer angle 

 of the canal be true or not, the transparent radiating tissue 

 which is implanted anteriorly into the capsule of the lens near 

 its border is covered with a distinct layer of homogeneous mem- 

 brane bearing the impress, as above described, of the ciliary 

 processes. 



The intimate structure of the lens is such as to favour 

 Helmholtz's view that adaptation to distance is principally 

 effected by the alteration of the figure of this body, increas- 

 ing or diminishing its convening power as the case may 

 require. 



It will be recollected that the band-like fibres passing 

 from the limbs of the tiiradiate fissure on one side to the 

 angles between them on the other are somewhat wed^e- 

 sbaped towards their extremities, with interlocking margins. 

 By this arrangement provision is made for the close approxi- 

 mation of the fibres by lateral pressure exerted through the 

 medium of the fluid in the canal of Petit, ensuring also an 

 equable convexity of the lens without dislocation of its struc- 

 tural elements ; and, what is most important, the definition is 



