148 THE THIED DAT. [CHAP. 



one is placed near the ciliary edge of the slit, and is 

 traversed by the efferent branch of the above-men- 

 tioned vascular loop. This vessel soon atrophies, and 

 with it the distal opening in the choroid slit completely 

 vanishes. In some varieties of domestic Fowl (Lieber- 

 kiihn) the opening however persists. The seam which 

 marks the original site of the choroid sht is at first con- 

 spicuous by the absence of pigment, and at a later 

 period by the deep colour of its pigment. FiaaUy, a 

 httle after the ninth day, no trace of it is to be 

 seen. 



Up to the eighth day the pecten remains as a simple 

 lamina; by the tenth or twelfth day it begins to be 

 folded or rather puckered, and by the seventeenth or 

 eighteenth day it is richly pigmented, and the pucker- 

 ings have become nearly as numerous as in the adult, 

 there being in all seventeen or eighteen. The pecten 

 is now almost entirely composed of vascular coUs, which 

 are supported by a sparse pigmented connective tissue ; 

 and in the adult the pecten is still extremely vascular. 

 The original artery which became enveloped at the 

 formation of the pecten continues, when the latter be- 

 comes vascular, to supply it with blood. The vein is 

 practically a fresh development after the atrophy of 

 the distal portion of the primitive vascular loop of the 

 vitreous humour. 



There are no true retinal blood-vessels. 

 The permanent opening in the choroid fissure for 

 the pecten is intimately related to the entrance of the 

 optic nerve into the eyeball; the fibres of the optic 

 nerve passing in at the inner border of the pecten, 

 coursing along its sides to its outer border, and radi- 



