32 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



coelom, or body cavity, and is destined to become the 

 pleural and peritoneal cavities. The mesoderm on 



Axial zone. . Neural canal. 



Lateral 



Cavity within somite. 



VUelline ; 

 Fig. 10. Transverse section of a sheep embryo, 17 \ days (Bonnet). 



Fig. ii. Rabbit embryo of the ninth day, seen from the dorsal 

 side (after Kolliker). The stem-zone (stz) and the parietal zone (ps) 

 are to be distinguished. In the former 8 pairs of primitive segments 

 have been established at the side of the chorda and neural tube; ap, 

 area pellucida; r/, medullary groove; vh, fore-brain; ab, eye-vesicle; 

 nth, mid -brain; hh, hind-brain; uiv, primitive segment; stz, stem -zone; 

 pz, parietal zone; h, heart; ph, pericardial part of the body cavity; vd, 

 margin of the entrance to the head-gut (vordere Darmpforte), seen 

 through the overlying structures ; fl/, amniotic fold ; vo, vena ompha- 

 lomesenterica. 



each side of the neural canal becomes symmetrically 



