MESODERM 



Fig. 234. Transverse sections of chick embryo with five pairs of somites. (This em- 

 bryo is slightly older than that shown in fig. 233; a topographical sketch of this develop- 

 mental stage is shown at the bottom of the figure with level of sections indicated.) Observe 

 that a dorsal arching (dorsal upgrowth) movement of the dorsal tissues is associated 

 with neural tube formation. See A and B. 



483 



