3 a 2 



MISS E. A. FRASER ON THE DEVELOPMENT 



front of the vena capitis meclialis and stretches laterally into the 

 intermediate mass (text-fig. 21, int.m.). The latter extends, on 

 the one hand, forwards and upwards to be connected by a narrow 

 band of cells with the m. obliqnus superior (text-fig. 21, o.s.) 

 and on the other, downwards and backwards to join the maxillo- 

 mandibular mesenchyme. 



Text-fio-ure 21. 



ih.i 





n.c Vp^ 







Fltascolarctos cineretis. G.L. 9 mm. 



Horizontal section through the head (S 4r-2-6) passing through the left head- 

 cavitj' {J.Ji.c), about a quarter of the way down, and showing the m. obliquus 

 superior (o.s.) growing forw ards from the intermediate mass (int.m.), this being 

 also united with the abducens muscle-mass (r.e.). In the next few sections 

 further veutrally, the intermediate mass is joined with the postero-lateral wall 

 of the head-cavity at approximately the region marked *. X 110 and reduced 

 byi. 



a.ca.=arteria cerebri anterior. JFJ?.= fore-brain. £r.F. = Gasserian ganglion. 

 7ijO. = hypoph3'sis. w.c.]-''. = naso-ciliary branch of the trigemiuai nerve. 

 ■w.ea.=vena cerebralis anterior. r.c.)B.=vena capitis medialis. III.=oculo- 

 motor nerve. 



The m. obliquus superior is a compact mass of cells lying 

 antero-laterally to the cavity above the optic cup. The intei-- 

 mediate mass a few sections below the level of text-fig. 21 is 

 attached to the extreme postero-lateral wall of the cavity. 



The oculomotor nerve runs down close to the postero-lateiiul 

 wall of the premandibular cavity (text-fig. 21, III.) and below the 

 level of the same splits np into many fibres near the point of 

 origin of the m. obliquus inferior. 



