Neat, — Nervous Syst. Squalus. 
PLATE 4. 
Figs. 18 and 21 magnified 23 diameters. Figs. 19 and 20 magnified 21 diameters. 
Fig. 18. An embryo with 52 somites (8 mm.). The otic capsule now lies opposite 
encephalomere VII. The thalamic and trochlear portions of the tri- 
geminus appear only as scattered clumps of cells. Posterior com- 
missure clearly differentiated. Between this andthe preceding stage 
the oculomotorius has appeared as a fibrillar process from the ventral 
wall of the midbrain, near gn. ms-ce. 
Fig. 19, An embryo with 65 somites (10 mm.). The chief peripheral branches of 
the cranial nerves have appeared; the abducens, asa process from the 
ventral wall of encephalomere VII. 
Fig. 20. An embryo with 78 to 80 somites (16 or 17 mm.). In this stage the ramus 
opthalmicus superficialis trigemini appears to have fibrillar relation 
with the mesoderm of the 2d somite, which is growing forward. The 
fibrous process of the abducens has come into relation with the 3d 
somite, and also is seen to have a branch passing to the mesoderm pos- 
terior to its place of origin. Most of the fibres of the ramus mandibu- 
laris trigemini appear in connection with encephalomere III. 
An embryo 21 or 22 mm. long. The trochlearis is now differentiated, and 
in relation with the musc. obliquus posterior. 
