OEGANS OF SENSE. 1*79 



the crystalline lens, enclosing, at their angle of sepa- 

 ration, the canal of Petit, which surrounds the peri- 

 pheral border of the lens. The vitreous humor, 

 which is adherent to the internal face of this mem- 

 brane, is an amorphous hyaline substance which, in 

 the fo3tus, contains oxal nuclei and stellate cells ; but 

 in the adult these cellular elements are no longer 

 visible, and nothing remains beyond an amorphous 

 jelly-like mass. 



The vitreous humor contains neither nerves nor 

 vessels. During foetal life its antero-posterior axis is 

 occupied by a tubular canal, containing a delicate 

 branch of the arteria centralis retinae sent forward to 

 the capsule of the lens ; after birth this canal becomes 

 obliterated. 



The crystalline lens is a solid body, surrounded by crystalline ie 

 a membranous envelope. This containing membrane, 

 or capsule, of the lens is highly transparent and 

 entirely destitute of structure, resembling a delicate 

 lamina of the purest glass. It possesses great elasti- 

 city, but is readily torn ; on the anterior surface of 

 the lens its thickness is ri <rth of a line, and posteriorly 

 but T loth of a line. It resists perfectly the action of 

 boiling water, a solution of potassa, and the acids. 

 Its external surface is continuous posteriorly with the 

 hyaloid membrane of the vitreous humor ; anteriorly 

 it is free ; its internal surface is lined by a layer of 

 exceedingly delicate polygonal cells, which, liquefy- 

 ing shortly after death, form the liquid of Morgagni.* 



* John Baptist Morgagni, the celebrated professor of anatomy at the 

 University of Bologna in Italy, and the preceptor of Scarpa, was born in 

 1682, and died in 1771. (Ed.) 



