1 62 Vertebrate Embryology 



Summary 



The most important events of the second 

 half of the second day are : 



1. The change in shape and position of the 

 optic vesicles. 



2. The origin of the unpaired rudiment of 

 the cerebral hemispheres from the front of the 

 fore-brain. 



3. The cranial flexure becomes visible. 



4. The auditory pits become deeper and 

 more pronounced. 



5. The curvature of the heart increases and 

 the rudiments of the auricles and bulbus arte- 

 riosus appear. 



6. The head-fold advances rapidly and the 

 tail- and lateral-folds make their appearance. 



7. The circulation of the vascular area is 

 definitely established. 



8. The amnion covers the head and neck of 

 the embryo, and its tail- and lateral-folds are 

 well marked. 



9. The first indication of the allantois is 

 seen. 



