THE ORGANS OF THE OUTER GERM-LAYER. 



461 



Fig, 262. — Cross section Enough the anterior part of tte trunk of an embryo of SoylUum, aft£V- 



Balfotjk. 



Between the dorsal wall of the trunk and its ventral wall, where the attachment of the stalk 

 of the yolk-sac is cut, there is stretched a thick richly cellular mesentery, which completely 

 divides the body-cavity into right and left halves. Within the mesentery the duodenum 

 (dii), from which, the fundament of the pancreas {pan) is given oflf dorsally and the funda- 

 ment of the liver (hp.d) ventrally, is twice cut through. In addition, the place where the- 

 vitelline duct [umbilical canal] (wttic) joins the duodenum is visible. 



sp.c. Spinal cord ; s.pg, ganglion of posterior root ; ar, anterior root ; dn, dorsally directed nerve- 

 springing from the posterior root ; mp, muscle-plate ; mp', part of the muscle-plate already 

 converted into muscles ; mp. I, part of the muacle-plate which gives rise to the muscles of the? 

 limbs ; ni, nervus latei:alis ; ao, aorta ; ch, chorda ; sy.g, sympathetic ganglion; ca.v, cardinal, 

 vein ; gp.n, spinal nerve ; sd, segmental (archinephric) duct ; st, segmental tube. 



