HISTOLOGICAL DEMONSTRATIONS. 133 



8. Outer limiting membrane. ~\ Cannot be 



9. Rods and cones (Jacob's membrane, or I clearly seen 

 the bacillary layer). [ in this pre- 



10. Pigmentary layer. J paration. 

 The pigmentary layer consists of the hexagonal pigment 



cells already examined ( 238), hitherto commonly regarded 

 as the inner layer of the choroid, but included by Max 

 Schultze as one of the layers of the retina, because of 

 delicate connective tissue fibrils, apparently connected with 

 the cells, passing inwards between the outer segments of 

 the rods and cones. 



24<DA. Examine the following preparations : a. V. S. 

 osmic acid retina of frog prepared as directed in 239, , 

 and cut by freezing. A power of 300 diam. will do, but 

 600 is much to be preferred. The rods being far larger 

 than in the cat's retina are easily seen, each consisting of 

 an outer and an inner segment. The former will probably 

 be much blackened by the osmic acid. It is normally as 

 clear as glass. The inner segment is seen perforating the 

 extremely thin outer limiting membrane. A cone is usually 

 seen with difficulty. Its outer segment is shorter than 

 that of the rod. 



b. (H.) Rods of frog's retina hardened in gold ( 239, c}. 

 Observe the outer segments of the rods cleaving transversely 

 into discs. The outer segments of a cone cleave in like 

 manner. According to Schultze the inner segments of rods 

 and cones are the true nerve terminations, while the outer 

 segments consist of columns of plates that play the part of a 

 reflecting apparatus. 



c. (L.) V. S. optic nerve entering eyeball, tinged with 

 carmine, showing the prominence (papilla] of the nerve, 

 its central blood-vessels, and the fibres of the lamina 

 cribrosa of the sclerotic, through the spaces between which 

 the nerve fibres enter the eyeball. 



d. (L.) V. S. from before backwards, of ciliary muscle, 

 iris, sclerotic, cornea, choroid and ciliary processes. The 

 anterior attachment of the muscle to the cornea is seen, and 

 its fibres are seen to spread out posteriorly on the choroid. 



e. (L.) Inner aspect of ciliary processes injected 

 opaque or transparent. 



