452 PRACTICAL DIEECTIONS. [APP. 



C. Removal of the embryo, as in II. C. and IV. C. 



The remarks made in the latter place apply with 

 still greater force to an embryo of the fourth and 

 succeeding days. 



D. Surface view of the transparent embryo. For 

 manipulation, vide IV. D. 



The points to be observed are : — ■ 



1. The formation of the fifth, seventh, and ninth 

 cranial nerves. 



To observe these, a small amount of pressure 

 is advantageous. 



2. The formation of the fourth visceral cleft, and the 

 increase in size of the superior maxillary process. 



3. The formation of the nasal pits and grooves. 



4. The great relative growth of the cerebral lobes and 

 the formation of the pineal gland from the roof of 

 the vesicle of the third ventricle. 



5. The great increase in the investing mass. 



6. The formation and growth of the muscle-plates, 

 which can now be easily seen from the exterior. 



7. The allantois. Make out its position and mode of 

 opening into the alimentary canal. 



E. The embryo as an opaque object. Manipulation 

 as II. F. For mode of examination vide 

 IV. E. 



The view of the mouth from underneath, shewing 

 the nasal pit and grooves, the superior and iuferior 

 maxillary processes and the other visceral folds and 

 clefts, is very instructive at this stage. Compare 

 Fig. 69. 



