346 



DEVELOPMENT OF EYE MUSCLES IN MARSUPIALS, 



EXPLANATION OF THE PLATES. 



Xietter 



mg. 



aln. = ali-uasal cavtilag'e. 

 cil.ff. = ciliary ganglion. 

 FJB. = fore-brain. 

 e. = eyeball. 

 I. = lens. 

 n.c.V. = naso-ciliary branch of the 



trigeminal nerve. 

 o.inf. = m. obliquus inferior. 

 op.c, = optic cup. 

 op.s. = optic stalk. 

 o.s. — m. obliquus superior. 



r.b. = ni. retractor bulbi. 



r.e. = m. rectus externus. 



r.i. = m. rectus internu.s. 



\inf. = m. rectus inferior. 



r.s. = m. rectus superior. 



III. = oculomotor nerve. 



IV. = trochlear nerve. 



V. = trigeminal nerve. 



VI. = abducens nerve. 



+ — band of mesodermal cells. 



Plate L 

 Tricliosurus vulpecula. G.L. 'J'o mm. (V. '01). 



Coloured drawing of v\'ax-plate model, posterior view, showing tlie 

 anterior (r.e.), and the posterior (r.6.) portions of the abducens muscle- 

 mass, the primordium of the m. obliquus inferior (o.ivf.) extending down 

 from thepostero-lateral corner of the solid mass of mesoderm representing 

 the former head-cavitj'. The primordium ot the m. rectus superior {r.s.) 

 stretches up above the optic cup from the dorso-lateral side of the same 

 mass. Nerve III. (III.) runs down just in front of the abducens muscle 

 complex and into the hinder end of the latter runs Nerve VI. (VI.) A 

 band of mesodermal cells ( + ) is seen to extend out towards the ventral 

 border of the eyelid. X 300 and reduced bj' -|. 



Anterior view, showing the primordium of the m. obliquus superior (o s.) 

 with its narrow prolongation lying anteriorly to the optic cup (oj9.c.), the 

 primordium of the m. rectus inferior (r.iiif.), extending forwards below the 

 optic stalk from the medial side of the m. obliquus inferior (o.inf.). The 

 primordium of the m. rectus superior (r.s.) is again seen. The naso-ciliary 

 branch (V.) of Nerve V. runs forwards below the m. obliquus superior. 

 Z=lens. The band of mesodermal cells { + ) extending out to the ventral 

 border of the eyelid is again seen. X 300 and reduced by i. 



Plate II. 



Tnchusurus vulpecula. G.L. 15 mm. 



Pig. 3. Coloured drawing of wax-plate model, anterior view, showing the m. obliquus 

 superior (o.s.), the m. obliquus inferior [o.ivf.], and the m. rectus inferior 

 {r.inf.) from which branches out the m. rectus internus {r.i.). Nerve IV. 

 (IV.) runs into the postero-medial side of the m. obliquus superior {o.s.). 

 X 150 and reduced by approximately |. 



4. Posterior view, showing the m. rectus superior (r.s.), the m. retractor bulbi 



(r.6.) still connected with the m. rectus externus (r.e.), and the m. obliquus 

 inferior {o.inf.) in which runs Nerve III. Nerve VI. is seen at the point 

 of union of the m. rectus externus and the m. retractor bulbi. A faint 

 dotted line indicates approximately the line of junction between the 

 m. rectus externus and the m. retractor bulbi. X 150 and reduced by 

 approximately |-. 



5. Ventral view, showing the distal end of the m. retractor bulbi (r.6.) which is 



growing forwards round the optic stalk, the m. obliquus inferior {o.inf.) 

 attached to the ali-nasal cartilage {aln.'), and the ciliary ganglion {cil.ff.) 

 lying below the optic stalk. Nerve III. is seen to run out from the 

 m. rectus inferior {r.inf.) into the m. obliquus inferior. X 150 and reduced 

 by approximately f . 



