416 JAMES ROLLIN SLONAKER 



tion is approximately 1.2 mm. The free inner margin is most 

 deeply pigmented and appears as a median crest or ridge 1.5 

 mm. long to which the lateral flutes or folds are attached. 



In a lateral view the shape and extent of the pecten is more 

 easily seen (fig. 2, plate 1). Its long, curved base, following the 

 curvature of the eyeball, is attached to the optic disc {Op N). 

 Its inner free margin also shows a slight cui^vature correspond- 

 ing to that of the base. This view shows the folds or flutes 

 very clearly. It is readily seen that there are a greater number 

 of folds at the base than at the free inner margin. The first 

 fold near the optic nerve entrance extends but a short distance 

 into the vitreous body. The second fold extends farther; the 

 third still farther, and the fourth practically reaches the median 

 crest or inner free margin of the pecten. Each of these four 

 folds are broader near their base and rapidly narrow as they 

 extend inward, until they blend with each other to form a com- 

 mon mass at the margin. The total number of folds at the base 

 of the pecten of the adult sparrow is twenty. Only sixteen of 

 these folds are of almost uniform length and extend from the 

 base to the median crest at the inner free margin. Wood ('14) 

 has overlooked the first two folds in his examination "of this 

 structure. 



The lateral extent and shape of these folds is shown in figure 

 3, plate 1, a section at right angles to figure 2, along the line 

 A-A. The folds are narrowed, both at the base where they 

 join the optic disc, and atthe free margin where they merge in 

 the crest. A portion of a section taken at right angles to figure 

 2 along the line B-B is shown in figure 4. This is also shown in 

 the microphotographs of sections in fig. 71, plate 12, and figs. 

 31 and 32, plate 6. The main bulk of the pecten is made up of 

 a thin, deeply pigmented membrane which is folded on itself 

 very much like the bellows of a camera. 



A small artery (a) extends from a basilary artery {ab) along 

 the middle of each of these folds. This basilar artery has been 

 previously described by Mihalkovics (73). These small arteries 

 in the middle of each' fold give rise to numerous branches which, 

 after forming a dense capillary network (fig. 3, c, plate 1) empty 



