THE ORGANS OF THE OUTER GERM-LAYER. 



Fig. 262. Cross section thioigh the anterior part of tl e trink of an embry of Scyllium, after 

 BALFOUR. 



Between the clorsal 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 

 (du), from which the fund xment of the pancreas (pan) is given off 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] (umc) joins the duodenum is visible. 



tp.c, Spinal cord ; s.pg, ganglion of posteiior root ; ar, anterior root ; dn, dorsally directed nerve 

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

 converted into muscles ; mp.l, part of the muscle-plate which gives rise to the mu-cles of the 

 limbs ; nl, nervus lateralis ; ao, aorta ; c/i. chorda ; sy.g, sympathetic ganglion ; ca.v, cardinal 

 vein ; sp./i, spinal nerve ; sd, segmental (archinephric) duct ; st, segmental tube. 



