7/2 GENERATION AND DEVELOPMENT. 



pouch, remaining for some time imperfect below, and 

 called the secondary optic vesicle. The deficiency below 

 contracts into what is called the ocular cleft, which subse- 

 quently becomes entirely obliterated. In connection with 

 the primary optic vesicle are developed the retina from, the 

 invaginated portion, and the pigmentary portion of the 

 choroid in connection with the outer part (fig. 236). In 

 the secondary optic vesicle the vitreous humour is formed. 

 The outer walls of the eyeball, the sclerotic and cornea, 

 are developed from the tissues immediately around those 

 which have been just described. 



The iris is formed rather late, as a circular septum pro- 

 jecting inwards, from the fore part of the choroid, between 

 the lens and the cornea. In the eye of the foetus of Mam- 

 malia, the pupil is closed by a delicate membrane, the 

 membrana pupillaris, which forms the front portion of a 

 highly vascular membrane that, in the foetus, surrounds 

 Fig. 238.* 



the lens, and is named the membrana capsulo -pupillaris. It 



* Fig. 238. Blood-vessels, of the capsulo -pupillary membrane of a 

 new-bom kitten, magnified (from Kolliker). The drawing is taken from 

 a preparation injected by Tiersch, and shows in the central part the 

 convergence of the net-work of vessels in the pupillary membrane. 



