24 THE EYE. 



processes, disposed in a circle and projecting into the anterior part of the vitreous 

 humour. These give attachment to the suspensory ligament of the lens. The 

 choroid coat is thickest behind, where it is pierced by the optic nerve. The outer 

 surface is connected to the sclerotic by loose connective tissue and by vessels and 

 nerves which pass obliquely across a lymph-space which otherwise serves to separate 



Fig. 26. CHOROID MEMBRANE AND IRTS EXPOSED BY THE REMOVAL OF THE SCLEROTIC AND CORNEA. 

 (After Zinn.) Twice the natural size. 



a, part of the sclerotic thrown back ; b, ciliary muscle ; c, iris ; e, one of the ciliary nerves ; /, one 

 of the vasa vorticosa or choroidal veins. 



Fig. 27. CILIARY PROCESSES AS SEEN FROM BEHIND. Twice the natural size. 



1, posterior surface of the iris, with the sphincter muscle of the pupil ; 2, anterior part of the 

 choroid coat ; 3, ciliary processes. 



the two tunics. The inner surface, which is smooth, is covered by the hexagonal 

 pigmented cells of the retina. These, when the retina is detached, generally remain 

 partly adherent to the choroid, and were formerly described as belonging to that 

 coat, but they are now known to be intimately related, both morphologically and 

 physiologically, to the retina. The ciliary part of the choroid with the ciliary 

 processes is often spoken of as the ciliary body (corpus ciliare). 



The ciliary processes (fig. 27), about seventy in number, are arranged 

 meridionally, and together form a circle. They consist of larger and smaller 

 thickenings without regular alternation. Each of the larger ones, measuring about 

 2*5 mm. in length and 0'6 mm. in depth, forms a rounded projection at its inner 

 (anterior) end, which is free from the pigment which invests the rest of the 

 structure ; but externally they gradually taper, and become lost. The smaller 

 processes are only half as deep as the others, and about one-third as numerous. At 

 and near the inner ends the processes are connected by lateral projections. 



Structure of the Choroid. The choroid consists mainly of blood-vessels 

 united by delicate connective tissue, which contains numerous large ramified and 

 pigmented cells. 



Externally the choroid is bounded by a non-vascular membranous layer similar 

 to the lamina fusca of the sclerotic, and known as the lamina suprachoroidea. This 

 is composed of thin membranes of a homogeneous aspect, but pervaded by networks 

 of fine elastic fibres, and covered by large flat cells. It contains also large flattened 

 pigment-cells dispersed irregularly or arranged in patches, with considerable intervals 



