[Proc. Roy. Soc. Victoria, 24 (N.S.), Pt. I., 1911.] 



Akt-VII. — On the Displacement of the Optic Lobes during 

 the DevelojJnient of the Brain of tlie Fowl. 



By K. K. OLIVER 



(Government Kesearch Scholar, Biological Department, University 

 of Melbourne). 



(With Plates XXV.-XXXV.). 



[Read 13th Jnly, 1911]. 



In the following paper a series of drawings is presented which 

 endeavours to illustrate clearly the manner in which the optic 

 lobes of the common fowl, Gallus domesticus, form and change 

 their position. The earliest drawing shows the mesence|3iialon 

 as a single median structure on the dorsal surface, and the sub- 

 sequent ones, its division into a bi-lobed structure, and its dis- 

 placement caused by the development and growth both of the 

 lobes themselves and of the adjacent parts. The later-stage 

 drawings depict the lateral and ventral course of the optic lobes 

 and their final attainment of the adult latero-ventral position. 

 No attempts at histological work have been made, the morpho- 

 logical relationships alone having been considered. 



Tlie search through a very large number of memoirs dealing 

 with the development of the brain has shown that the literature 

 •on this subject is concerned almost entirely with histological 

 work, and I have been able to find very few references to the 

 particular aspect of the work with which this paper deals. 



A. Milnes Marshall in his " Vertebrate Eimbrvology,'' p. 256, 

 mentions the fact that the mesencephalon, till the end of the 

 4th day of incubation, remains approximately spherical, and on 

 the 5th the optic lobes begin to form ; also that on the l-Gth 

 day the optic lobes begin to become pushed apart, and take 

 up their adult position. 



Frank K. Lillie, in " The Development of the Chick,'' men- 

 tions the formation of the optic lobes, but in connection with a 

 detailed account of the rest of the brain onlv. A consecutive 



