346 ORR. ' [Vol. I. 



stalk of this side. In later stages the chiasma comes to lie 

 outside the surface of the brain. At that time, in transverse 

 sections the anterior band is very distinct, and is completely 

 separated from the chiasma in the median line ; but laterally 

 the optic fibres from the chiasma run into the lateral continua- 

 tions of the anterior band, i.e., the lateral bands. 



In Fig. 62, F, may be seen the posterior commissure {PCs) 

 in lateral section. This is the only commissure of the brain 

 which is complete at this stage. Its fibres are continued 

 dorsally in a broad band lying superficially across the roof of 

 the brain. At the anterior edge of this band is the rudiment 

 of the pineal eye. The latter has acquired a lumen, but is 

 otherwise unchanged from the condition shown in Fig. 54 E. 

 Anterior to the pineal eye, the roof of the thalamencephalon 

 is a thin layer of cubical cells; and just behind the lobes of 

 the secondary fore-brain it shows a number of small, round, 

 gland-like outgrowths. About half-way between the posterior 

 commissure and the optic chiasma is a small band of fibres 

 extending dorsally from the lateral band and ending in a 

 point. (This is represented in the drawing, but not lettered.) 

 None of these fibres cross over the roof of the brain. From its 

 position, I judge this pointed band to be the rudiment of the 

 superior commissure described by Osborn in several amphibia, 

 and by Shipley in Pctromyson. About half-way between the 

 rudiment of the superior commissure and the chiasma lies 

 another band of fibres, extending dorsally into the anterior wall 

 of the secondary fore-brain. At this stage I find no trace of 

 these fibres uniting across the median line with fibres from the 

 band of the opposite side ; but they undoubtedly form, later, the 

 anterior commissure. In embryos of the frog and Amblystoma, 

 at a stage apparently corresponding to this stage of Anolis, I 

 find the general features of the lateral and anterior bands, and 

 their relation to the optic fibres, to be about the same as above 

 described ; but in the amphibian embryos the fibres which run 

 dorsally from the lateral bands, just behind the optic stalks, 

 unite across the anterior surface of the brain, forming a super- 

 ficial commissure a short distance dorsal to the optic stalks ; 

 therefore I think there can be no doubt that the corresponding 

 fibres in the brain of the lizard are the rudiments of the anterior 

 commissure. 



