322 



MISS E. A. PRASER ON THE DEVELOPMENT 



Text-figure 17. 



a.c.a. 



LAc. 



Ti'icJiostirus vulpecula. G.L. 9'5 mm. (V. '01). 



Horizontal section through the head (S 4^3-5), passing through the optic cup (op.c), 

 optic stalli {op.s.) and lens (?.), and showing the hist vestige of the left head- 

 cavity (l.h.c.) and the proximal end of the m. obliquus inferior {o.inf.), into 

 which fibres of the oculomotor nerve (111.) penetrate. The two portions (r.6. 

 & r.e.) of the abduceus rauscle-mass are well seen and are penetrated bj' the 

 abducens nerve (VI.). X 110 and reduced by 5. 



a.c.a. —arteria cerebri anterior. i^i?.= fore-brain. ^.K = Gasserian ganglion. 

 M..C. F.=naso-ciliary branch of the trigeminal nerve. v.c.m. = YQX\a. capitis 

 medialis. 



Embrvos of G.L. 11 mm., 11*5 mm., & 12 mm. (= Stages XII. 

 & XIII.). (Text-fig. 18.) 



The observations were made from six embryos, one of 11 mm. 

 (XII. '04), four of 11-5 mm. (XXII. '04, 5 '97, 9 '98, & VII. '01), 

 and one embryo of 12 mm. (X. '01). 



The lumen of the optic stalk is very small and the cavity of 

 the lens is considerably reduced compared with the 10 mm, stage. 



A thick strand of cells running postero-medially towards the 

 hypophysis on each side of the fore-brain is all that remains of 

 the unused walls of the former head-cavity. With the lateral 

 end of this strand is connected the m. rectus superior which, 



