OF THE EYE MUSCLES IN MARSUPIALS. 



323 



running dorsally outwards, ends above the eye just behind the 

 middle of the latter (text-fig. 18, r.s.). 



The m, rectus inferior (text-fig. 18, r.inf.) arises below the 

 proximal end of the m. rectus superior with which it is joined 

 by a slender connection ; it has increased in thickness and passes 

 out ventrally and anteriorly below the optic stalk. Behind the 

 middle r-egion of this muscle, towards its proximal end, a small 

 new oftshoot branches out and stretches up dorsally on to the 

 anterior side of the optic stalk ; this is the first appearance of 

 the m. rectus internus (text-fig. 18, r.i.). 



;vVvv, 





-n.c.V. 





TricJiosurus vulpecula. G.L. ll'o mm. (5 '97). 



Longitudinal section (S 11-3-5), showing the primordium of the m. rectus internus 

 (r.i.) which develops as an outgrowth from the m. rectus inferior {r.inf.). 

 The m. rectus externus (r.e.), m. rectus superior {r.s.), and m. obliquus superior 

 {o.s.) are also seen. X 110. 



_g'.F.=Gasserian ganglion. «..c.F'.=naso-ciliary branch of trigeminal nerve. 

 oj>.s. = optic stalk. II I. = oculomotor nerve. VI. =abducens nerve. 



The m. obliquus inferior has changed most in position compared 

 with the last stage. It has moved forwards below the bulbus 

 and now runs antero-ventrally ovitwards, lying some distance in 

 front of the m. obliquus superior above. It is loosely joined to 

 the outer ventral end of the m. rectus inferior, though this 

 connection is nothing more than a few strands in the 11-5 mm. 

 embryo, and its distal end has begun to turn slightly forwards 

 towards the ali-nas?J cartilage from which it finally takes its 

 origin. 



The m, obliquus superior is now well developed ; it has 



