234 



ANIMAL PHYSIOLOGY. 



a distinct degree of force, 

 because the anterior wall 

 of its capsule is strong 

 and elastic: the posterior 

 wall is fused with the hya- 

 loid membrane. The pli- 

 cated collar outside the 

 capsule of the lens is called 

 the zonule of Zinn; and if 

 a small tube be gently 

 pushed into it near to its 

 inner edge, and air be 

 blown in, there will be 

 seen to be a cavity sur- 

 rounding the periphery of 

 the capsule, the anterior 

 wall of which is formed by 

 a plicated fibrous mem- 

 brane distinct from the 

 hyaloid. This cavity is 

 called canal of Petit; and 

 f x the membrane in front of 

 i>* it, extending from the 

 most prominent part of the 

 hyaloid membrane to the 

 anterior wall of the capsule 

 of the lens, is named the 

 H*. : (^/suspensory ligament. 



The crystalline lens is 

 about a third of an inch in 

 diameter, and a fifth from 

 front to back, and is more 

 convex behind than in 

 front. It consists of layers 



Fig. 118. RETINA, diagrammatic view of the structures seen in 

 vertical section. A, General view. B, The nervous elements. 

 a, Bacillary layer; 6, membraiia limitans externa ; c, external 

 nuclear layer ; d, external granular layer ; e, internal nuclear 

 layer ; /, internal granular layer; g, ganglionic layer ; h, 

 branches of optic nerve ; f, membrana limitans interna. After 

 Schultze. 



