THE VASCULAR TUNIC. 



H55 



sharply inward and floats in the aqueous humor, incompletely dividing the space 

 anterior to the crystalline lens into a posterior and an anterior chamber. 



The Choroid. The choroid (tunica chorioidea) forms the posterior two-thirds 

 of the vascular coat. It lies between the sclera and the retina and extends from the 

 optic nerve entrance to 



the anterior limit of the FlG - I20 9- 



visual part of the retina 



at the ora serrata, its 

 main function being to 

 supply nutrition to the 

 nervous tunic. It is 

 a delicate coat, which 

 has a thickness of . i 

 mm. near the nerve and 

 gradually diminishes in 

 thickness towards the 

 ora serrata, where it 

 measures only .06 mm. 

 The outer surface is 

 roughened by the tra- 

 beculae of connective 

 tissue which cross the 

 suprachoroidal lymph- 

 space and connect the choroid with the overlying sclera. The connection is main- 

 tained partly also by the larger vessels and nerves, which lie within this space 

 during their course forward and send branches to supply the choroid. The inner 



FIG. 1210. 



Choroidal 

 stroma 

 Lamina su- 

 prachorioidea 

 Suprachoroi- 

 dal space 

 Lamina fusca 

 of sclera 



Section of choroid. X 275. 



Large vein 



Artery 



Surface view of injected human choroid, showing venous radicles converging to form larger veins. X 18. 



surface of the choroid is smooth and covered by the pigmented cells of the retina, 

 which are so closely attached that they frequently adhere to the choroid when the 

 membranes are separated. Posteriorly, the choroid helps to form the lamina crib- 

 rosa, the fenestrated membrane through which the optic nerve-fibres pass ; anteriorly 

 it is continuous with the ciliary body. 



