THIRD TUNIC. 



449 



of its area. The posterior layer is of a deep purple tint, and is thence 

 named uvea, from its resemblance in colour to a ripe grape. 



The Ciliary processes may be seen in two ways, either by removing the 

 iris from its attachment to the ciliary ligament, when a front view of the 

 processes will be obtained, or by making a transverse section through the 

 globe of the eye, when they may be examined from behind, as in fig. 201. 



The ciliary processes consist of a number of triangular folds, formed 

 apparently by the plaiting of the middle and internal layer of the choroid. 

 According to Zinn, they are about sixty in number, and may be divided 

 into large and small, the latter being situated in the spaces between the 

 former. Their periphery is connected with the ciliary ligament, and is 

 continuous with the middle and internal layer of the choroid. The central 

 border is free, and rests against the circumference of the lens. The ante- 

 rior surface corresponds w r ith the uvea; the posterior receives the folds of 

 the zonula ciliaris between its processes, and thus establishes a connexion 

 between the choroid and the third tunic of the eye. The ciliary processes 

 are covered with a thick layer of pigmentum nigrum. which is more 

 abundant upon them, and upon the anterior part of the choroid,. than upon 

 the posterior part. When the pigment is washed off, the processes are of 

 a whitish colour. 



THIRD TUNIC. The third tunic of the eye is the retina, which is pro 

 longed forwards to the lens by the zonula ciliaris. 



Dissection. If, after the preceding dissection, the choroid membrane 

 be carefully raised and removed, the eye being kept under water, the 

 retina may be seen very distinctly. 



* The anterior segment of a transverse section of the globe of the eye, seen from 

 within. ^ 1. The divided edge of the three tunics ; sclerotic, choroid (the dark layer), 

 and retina. 2. The pupil. 3. The iris, the surface presented to view in this section 

 being the uvea. 4. The ciliary processes. 5. The scalloped anterior border of the 

 retina. 



f The posterior segment of a transverse section of the globe of the eye, seen from 

 within. 1. The divided edge of the three tunics. The membrane covering the whole 

 internal surface is the retina. 2. The entrance of the optic nerve with the arteria cen- 

 tialis retinae piercing its centre. 3, 3. The ramifications of the arteria centralis. 4. Th 

 foramen of Soemmering, in ths centre of the axis of the eye ; the shade from the sides 

 of the section obscures the limbus luteus which surrounds it. 5. A fold of the retina 

 which generally obscures the foramen of Soemmering after the eye has been opened 



