THE EMBRYOLOGY OF THE EYE. 45 



rest the capillaries. The first change that oc- 

 curs in the formation of the choroid is the 

 arraneement of a considerable number of cells 

 of various shapes about the capillaries and 

 the development of a number of larger vessels 

 just external to the capillaries. These changes 

 all take place between the pigment-epithelium 

 and the fibrous layer which is the rudiment- 

 ary sclera, the latter being simply pushed 

 outward by the development of the choroid 

 beneath it. 



After the appearance of the larger vessels, 

 pigmented cells are seen just beneath the ru- 

 dimentary sclera at the outer margin of the 

 rudimentary choroid, and later pigmented 

 cells are found deeper in the choroid, until 

 finally in the pig they reach up to the capil- 

 lary layer. In man the pigmented cells seldom 

 extend into Sattler's layer of smaller vessels, 

 and almost never reach the capillaries. The 

 pigment is in the form of rods, shorter and 

 more rounded at the ends than the rods in the 

 pigment-epithelium. 



