240 



STUDY OF PIG EMBRYOS. 



Pig Embryo of 20 mm. 



Sections of this stage are figured. In the practical laboratory work em- 

 bryos a little larger or smaller may serve equally well to illustrate the develop- 

 mental conditions of this stage. 



Transverse Section through the Snout.— The parts shown are the same as in 

 figure 146, to the description of which reference is made. The present figure 140 



a v.d. 



a v.s. 







I: . 



In.. 139.— Fig, 17.0 mm. Frontal Series 39, Section 63. 



All, Allantois. Art, Umbilical artery. A.vi, Vitelline artery. Ca, Ccelorn. Ec, Ectoderm. //, Ileum, ma, 



Mesenchyma. C.V.D, Right umbilical vein. U. !'. S, Left umbilical vein. X 35 diams. 



is added to illustrate the development of the palate shelf, Pal. The palate shelf is 

 a large protuberance on the inner side of the maxillary process. Its inner edge 

 abuts against the tongue, Ton, and its upper edge underlies the maxillo-turbinal 

 fold, max. th, and its lower edge forms part of the roof of the oral cavity, Or. At 

 this stage it consists of a large mass of undifferentiated mesenchyma, covered by 



