OF THE EYE MUSCLES IN MARSUPIALS. 



309 



the head-cavity close to the postero-lateral wall of the latter, its 

 lateral end running into the intermediate mass, the limits of the 

 two being- indistinguishable (text-fig. 6, int.m., and also the 

 ventral end in text-Hg. 4, int.m.). The intermediate mass itself, 

 wdiich is composed of more loosely connected cells, p'^sses on the 

 one hand, forwards into a mass of condensed mesenchyme lying 

 above the optic vesicle on the outer side of the ophthalmic nerve, 

 this portion representing the primordium of the m. obliquus 

 superior (text-fig. 6, o.s.) ; and on the other hand, backwards and 



Text-fio-ure 6. 



i/.c.a 



Tricliosums vulpecula. G.L. 7 mm. (a '97). 



Horizontal section (somewhat diagrammatic) througli the head (S 3-1-11), showing 

 the posterior {r.b.) and anterior (r.e.) portions of the abducens muscle-mass of 

 the left side, which extend in front of the vena capitis medialis [v.c.m.), just 

 ventral to the vena cerebralis anterior (v.c.a.), to unite with the intermediate 

 mass {int.m.). The primordium of the m. obliquus superior (o.s.) is se^n as a 

 forward outgrowth from the intermediate mass. Owing to the obliquity of 

 the sections, the right side is cut at a more dorsal level than the left and only 

 shows the posterior portion (r.b.) of the abducens mass lying medial to the 

 vena capitis medialis (v.c.m.) and the vena cerebralis anterior {v.c.a.). X 75 and 

 reduced by I . 



a.c.a.=arteria cerebri anterior. l.7i.c.=le{t head-cavity. «i;.=notochord. 



downwards lateral to the vena capitis medialis and is loosely 

 connected with the maxillo-mandibular muscle-mass, the con- 

 nection here not being well seen. The union of the intermediate 

 mass with the postero-lateral wall of the cavity is most probably 

 again present. 



The oculomotor nerve is now thicker and its distal end 

 terminates dorso-laterally to the head-cavity. 



