OF THE EYE MUSCLES IN MARSUPIALS. 



319 



Further ventvally the cavities have completely disappeared and 

 from the now solid mass of ceils the m. obliquus inferior runs 

 outwards and downwards behind the eye (text-fig. 15, o.ii)f.). 

 Immediatel}^ medial to the m. obliquus inferior the difterentiation 

 of cells destined to become the m. rectus inferior extends down- 

 wards, its ventral end turning anteriorly, medial to the bulbus 

 and below the optic stalk. 



Text-figure 15. 



r.s. s.o.V. 



\ * 





o.S. 





r.e 



o in f- 



Tricliosurus mdpecuJa. G.L. 8'5 mm. ('97). 



Longitudinal section (S 3-2-8), showing the ni. obliquus superior (o.s.) with its 

 narrow posterior prolongation and the m. obliquus inferior [o.inf.) extending 

 below the optic cup {op.c). The distal end of the m. rectus superior {r.s.) and 

 the lateral side of the anterior portion (r.e.) of the abducens muscle-mass are 

 also seen. X 110. 



^.F. = Gasserian ganglion. jt.c.F.=naso-ciliary branch of V. s.o.F.=supra- 

 orbital branch of V. mx. P''. = maxillary branch of V. 



The primordium of the m. obliquus superior is now established 

 as an independent structure. Its main portion forms a con- 

 densed mass of cells lying anterior and dorsal to the eye, and 

 from this a narrow prolongation projects posteriorly above the 

 bulbus, the higher pointed end of which comes very close to the 

 m. rectus superior (text-fig. 15, o.s.). This backward prolongation 

 is obviously the last remnant of the former connection with the 

 intermediate mass (compare Johnson, '13, p. 150). The last 



