OF THE EYE MUSCLES IN MARSUPIALS. 



317 



from the mid-brain, runs close to the postero-latercal wall of the 

 cavity between the latter and the abducens mass (text-figs. 9 cfe 12, 

 III.). At its distal end it breaks up into many fibres which 

 extend into the postero-lateral proliferation near the point of 

 origin of the m. ol)liquns infei'ior. 



'J'ext-fiyure 13. 



op. c -r«- 







,'.% 



,$"■» 







max.md. 







\/.O.I . 



Trichosurtig vulpecula. (XIF a. '02.) 



Longitudinal section (S 11-1-4), passing through the lateral wall of the cavity and 

 the priiDOvdiura of the m. obliquus inferior (o.inf.). The primordium of the 

 m. obliquus superior (o.s.) extends forwards from the intermediate mass 

 (inf.m.) as a solid band of cells dorsal to the optic cup (o^'c). X 110. 



^.'F'. = Gasserian ganglion. »naj'.wi.=maxillo-mandihular mesenchyme. n.c.F.= 

 naso-ciliary branch of the trigeminal nerve. u.o.j. = vena orbitalis inferior. 



Embryo of G.L. 8-5 mm. ('97 Sz lY.'Ol) ( = Stage IX. a & h). 

 (Text-figs. U-16.) 



This stage, which measures 8-5 mm. and of which we have 

 two embryos, (a) and (b), is a good deal more advanced than the 

 preceding one. 



The primary optic vesicle still shows a well-marked cavity in 

 the region of attachment of the optic stalk which is still hollow, 

 and pigment is beginning to form in its outer wall. The inner 

 wall of the Ions is thickened, its cavitj' being reduced to a narrow 



