294 JAMES ROLLIN SLONAKER 



The elongated base at this age measures 0.390 mm. long and 

 0.187 mm. broad, and the cone extends 0.102 mm. into the 

 vitreous body. This corresponds closely to the condition in the 

 six-day chick as described by Froriep. He says that at this age 

 this roll has widened and extends into the vitreous chamber 

 as a thick leaf or ridge. The large blood-vessel which remains 

 in the base of this ridge is later called the pectineal artery. It 

 sends smaller vessels up into this flat projection where they are 

 most numerous at the margin or free edge. The ridge is attached 

 to the wall along the fissural groove. 



"6pN ' 

 7 



Text fig. 7 Enlarged diagrammatic drawing of a cross-section of the early 

 stage of the developing pecten as seen in the seven-day sparrow embryo. C-S, 

 developing chorioid and sclerotic layers; E, pigment epithelium; M, mesoderm; 

 P, pecten; OpN, optic nerve; R, retina. 



Text fig. 8 Enlarged diagrammatic drawing of a cross-section of the de\el- 

 oping pecten in the eight-day sparrow embryo. OpN, optic nerve; F, pecten. 



At the age of about eight days this flat projection has grown 

 much farther into the vitreous body, and has become thinner. 

 The cells still show no differentiation and are uniformly distri- 

 buted throughout the main bulk of the growth. This is shown 

 in text-figure 8, P, and figure 67, P. Spindle-shaped cells are 

 seen in the optic-iierve region. Among these are scattered 

 numerous cells similar to those forming the pecten. 



By the twelfth day of incubation the pecten has greatly 

 increased in dimensions. Its earlier broad form has been changed 

 to a flattened, plate-like mass of almost uniform thickness 

 (text-fig. 9, P, and fig. 76, P). Its length is now 0.8650 mm. 



