No. 2.] EMRRYOLOGV OF THE LIZARD. 345 



fibres {LF) passing forward to meet the opposite band just 

 vertical to the chiasma {Ch). A comparison of the distance 

 between the ventral parts of the fore- and hind-brain in the two 

 sections (62, F, and 6},, F) will give an idea of the transverse 

 curve of the ventral surface of the brain. Owing to this curve 

 and the anterior diminution of the basal breadth of the brain, 

 the lateral band passes out of the plane of section 62, F, before 

 reaching the anterior surface of the brain. 



Before the last trace of the lumen of the optic stalk has 

 disappeared, the decussation of the fibres of the optic nerves 

 becomes apparent. The fibres of the dorsal edge of the lateral 

 band, as they pass across the anterior surface of the brain 

 towards the root of the optic stalk on the other side, bend 

 dorsally, and running along the anterior wall of the stalk spread 

 over the lateral wall of the eye-cup. Where the fibres from 

 opposite sides meet, those from each region resolve them- 

 selves into four or five flattened bundles, and cross in such a 

 way that between each two bundles of one nerve lies a bundle 

 from the opposite nerve. I have searched in vain for any traces 

 of fibres running from the lateral band into the optic nerve of 

 the same side. None such appear. At this time the chiasma 

 lies within the general superficial surface of the brain, its flat 

 outer surface corresponding with the surface of the brain, 

 while its inner surface is rounded. The ventral edge of the 

 chiasma is at first continuous with the dorsal edge of the 

 anterior band {LF), but later a wedge-shaped growth of 

 cells pushes in between the two edges. Fig. 64, F, is an 

 enlarged view of the region of the chiasma in the same 

 section that is pictured at 6^, F. Here the chiasma {C/i) 

 and the anterior band are seen still touching each other, while 

 at the same time they are marked off from each other by a wedge- 

 shaped protrusion of the cells of the brain-wall. Later this 

 wedge-shaped protrusion increases in size, and completely sepa- 

 rates the two parts in the median line. By following the courses 

 of these two fibrous parts in the consecutive sections between 

 sections 63, F, and 62, F, it is found that the anterior band 

 (LF) is perfectly continuous with the lateral band (LF, Fig. 

 62, F), and that the bundles of the chiasma coming from the 

 opposite optic stalk also unite and blend with the lateral band ; 

 while the bundles from the other lateral band run into the optic 



