522 ANATOMICAL TECHNOLOGY. 



not extend cephalad of the iris. Opposite the white zone it is folded 

 into plaits (Plicae ciliares, Fig. 126). There are about seventy of 

 these plaits or folds. 



1423. Iris. The iris, as stated above, is the circular perforated 

 curtain caudad of the cornea. Its caudal surface is black, its 

 cephalic a golden yellow, which gives color to the eye. It is at- 

 tached at its circumference to the choroidea, the cornea and the 

 sclerotic. 



1424. Retina (Fig. 126). The retina is the ental coat or tunic 

 of the eye. It is an expansion of the optic nerve to which are added 

 nerve cells and various other parts (see Quain, A, II, 605). It is the 

 sensitive part of the organ of sight. It may be separated from the 

 choroid as shown in Fig. 126 by using a scalpel handle. Note that 

 it is of nearly uniform thickness until it reaches the margin of the 

 ciliary folds, Ora serrata (Fig. 126). Its extension upon the folds 

 becomes thin and is called the Pars ciliaris retina. The entrance 

 of the optic nerve appears as a round white spot, macula lutea 

 (blind spot). 



1425. Tapetum (Fig. 126). In the eye of the cat, as in many 

 other animals, the retina does not contain pigment over its whole 

 extent, but is devoid of it in its dorso-mesal part. Here the cho- 

 roid is brilliantly colored, forming the so called Tapetum. The 

 color is metallic golden-blue green. In this part of the choroid is a 

 deposit of mineral salts of calcium which assists in giving the lumi- 

 nous appearance to the cat's eye in a dim light (Milne-Edwards, XII). 



1426. Humor aqueus. The aqueous humor is a clear watery 

 fluid which fills the space between the cornea and the iris and lens 

 and also the small space between the iris and the plicae ciliares (Fig. 

 126). These spaces are called, from their position, Camera aquosa 

 cephalica (anterior), cephalic or anterior aqueous chamber (Fig. 126, 

 C. aq.), and Camera aquosa caudalis (posterior), caudal or posterior 

 aqueous chamber (Fig. 126, C. a.). 



1427. The corpus vitreum or vitreous humor is a transparent 

 jelly-like substance occupying the greater space of the eyeball. It 

 is bounded cephalad by the lens and ciliary processes and at all 

 other points by the walls of the eyeball. 



1428. Lens (lens crystallina) Crystalline lens (Fig. 126). 

 The lens is the double convex transparent body situated between the 

 aqueous chambers and the vitreous body. Its cephalic convexity 



