DEVELOPMENT OF THE EYEBALL. 605 



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

 lens and the cornea. In the eye of the foetus of Mammalia, 

 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 the lens, and is named 

 the membrana capsulo-pupillaris. It is supplied with blood by 



FIG. 238. 



Bloodvessels of the capsulo-pupillary membrane of a new-born kitten, magnified 

 (from Kolliker). The drawing is taken from a preparation injected by Tiersch, and 

 shows in the central part the convergence of the network of vessels in the pupil- 

 lary membrane. 



a branch of the arteria centralis retince, which, passing for- 

 wards to the back of the lens, there subdivides. The mem- 

 brana capsulo-pupillaris withers and disappears in the human 

 subject a short time before birth. 



The eyelids of the human subject and mammiferous animals, 

 like those of birds, are first developed in the form of a ring. 

 They then extend over the globe of the eye until they meet 

 and become firmly agglutinated to each other. But before 

 birth, or in the Garni vora after biHh, they again separate. 



The ear likewise, according to Huschke, consists of a part 

 developed from within, and of one formed externally. The 

 labyrinth is developed upon the hollow protruded part of the 

 brain which forms the auditory nerve. It appears first in the 

 form of an elongated vesicle at the hinder part of the head of 

 very young embryos above the second so-named branchial 

 cleft. From it is developed a second vesicle, the rudiment of 

 the cochlea, the convolutions of which are then formed. The 



51 



