338 



MANUAL OF HISTOLOGY. 



easily contracted in diameter by any increase in intra-ocular 

 pressure. 



The arteries of the sclera, with their thick adventitial coats, 

 the peculiar sheaths of the veins and capillaries, as also the 

 nerves, are best studied in hematoxylon preparations. A solu- 

 tion of silver nitrate (a quarter to one per cent.) will expose 

 the endothelial cells, while sections of the tissue may be 

 made from specimens preserved in alcohol or Miiller' s fluid. 



The tunica vasculosa, consisting 

 of the choroid, ciliary body, and 

 iris, forms one continuous mem- 

 brane through which the principal 

 blood-supply of the eye is carried. 

 The choroid. This tunic lines 

 >cAthe sclera from the entrance of the 

 optic nerve to the junction of sclera 

 and cornea, and is united to it at 

 those points ; over the remaining 

 portion there is a loose connection 

 formed by scattered fibres and the 

 numerous vessels and nerves which 

 pass through the sclera to the cho- 

 roid. The meshes of the open 

 network between the layers of 

 the choroid and the sclera form 

 lymph-sacs the perichoroidal 

 spaces which connect with the sac 

 enclosed in Tenon's capsule, and 

 this in turn unites with the su- 

 pra-vaginal space surrounding the 

 sheath of the optic nerve. The 

 choroid consists of several layers, 

 with limits not distinctly marked. 

 The lamina suprachoroidea (Fig. 154, sc) lies next the 

 sclera, and consists of fine elastic and connective-tissue fibres, 

 holding in their meshes pigmented and transparent cells: 

 the first are stellate, often with projecting arms by which 

 several are joined together ; the latter resemble lymph-cor- 

 puscles. 



The layer of large vessels is traversed by branching arteries 

 and veins ; between them are numerous pigmented corpuscles, 



Fio. 15-1 Sclera, * ; choroid, cA ; ret- 

 ina, >; perichoroidal space, /xA; lamina 

 Bnprachoroidea, c ; lamina chorio-capilla- 

 ri, ex; ; lamina vitrea, c ; layer of pigment- 

 celU between cboroid and retina, p. After 

 Merkel. 



