144 



THE DISSECTION OF PIG EMBRYOS 



forceps now remove the ventral body wall. By tearing open the wall of the umbiKcal cord 

 along ojie side it may be removed, leaving the intestinal loop intact. Pull away the heart, 

 noting'its external structure. The liver may also be removed, leaving the stomach and in- 

 testine uninjured. A portion of the septum transversum covering the lungs may be care- 

 fully stripped away and the lungs thus laid bare. 



Dissections made in this way show the trachea and lungs, the esophagus, 

 stomach and dorsal attachment of the septum transversum, the course of the 

 intestinal canal, and also the mesonephroi and their ducts. Favorable sections 

 through the caudal end of the body may show the urogenital sinus, rectum, and 



MidUrian duct aiihiiic 



Tracliea 



Si'pliim transversum 

 Slomach 



lilcsoncphric duel 

 Mcsoiicphros 



Vmliilical artery 

 Rcclitni 



Ccelo 



Fig. 148. — Ventral dissection of a 15 mm. pig embryo, showing lungs, digestive canal and mesonephroi. 

 The ventral body wall, heart and liver have been removed and the limb buds cut across. X 6. 



sections of the umbilical arteries and allantois (Figs. 97, 124 and 148). In late 

 stages, by removing the digestive organs, the urogenital duds and glands are beau- 

 tifully demonstrated (Figs. 223 and 224). 



DEVELOPMENT OF THE FACE 



The heads of pig embryos have long been used for the study of the development of the 

 face. The heads should be removed by passing the razor blade between the heart and adja- 

 cent surface of the head, thus severing the neck. Next cut away the dorsal part of the head 

 by a section parallel to the ventral surface, the razor blade passing dorsal to the branchial 

 clefts and eyes. Mount, ventral side up, three stages from embryos 6, 12, and 14 mm. long, 

 as shown in Figs. 97 and 149. 



In the early stages (Figs. 97 and 124) the four branchial arches and clefts 

 are seen. The third and fourth arches soon sink into the cer\'ical sinus, while 

 the mandibular processes of the first arch are fused early to form the lower jaw. 

 Laterally the frontal process of the head is early divided into lateral and median 



