THE ANATOMY OF TEN TO TWELVE MM. PIG EMBRYOS 



119 



Trachea and Lungs. — Caudal to the fourth pharyngeal pouches the esoph- 

 agus and trachea separate and form entodermal tubes (Figs. 122 and 123). 

 Cephalad of the point where the trachea bifurcates to form the primary bronchi 

 there appears on its right side the tracheal bud of the upper lobe of the right lung 

 (Fig. 124). This bronchial bud is developed only on the right side and appears in 

 embryos of 8 to 9 mm. Two secondary bronchial buds arise from the primary 

 bronchus of each lung, and form the anlages of the symmetrical lobes of each lung. 



Lateral nasal process 

 Lacrymal groove 



Maxillary process 

 Mandibular process 



Cervical sinus 

 Trachea 



Tracheal lung bud 



Upper limb bud 



Septum transversum 



Hepatic diverticulum 



Yolk sac 



Yolk stalk 



Allantois -^ 

 R. umbilical artery ^ 



Lower limb bud 



Olfactory pit 



Eye 



Median nasal process 



— Branchial arch 2 



-^Branchial arch 3 



Branchial arch 4 



-L. lung 

 ~ Esophagus 

 ~ Stomach 



-Mesonephric duct 



~ Ventral pancreas 



~ Mesonephros 



-^Cephalic limb of intestine 



^Caudal limb of intestine 



^Rectum 



^Metanephros 



Mr^niicphric duel / ^P'""' '"'"'^ 



Rectum 



Fig. 124. — Ventral dissection of a 9 mm. pig embryo. The head is bent dorsad. X 9. 



Esophagus and Stomach. — The esophagus extends as a narrow tube caudal 

 to the lungs, where it dilates into the stomach. The stomach is wide from its 

 greater to its lesser curvature and shows a cardiac diverticulum (Lewis). The 

 pyloric end of the stomach has rotated more to the right, where it opens into the 

 duodenum, from which division of the intestine the Uver and pancreas develop. 



The liver, with its four lobes, fills in the space between the heart, stomach, 

 and duodenum (Fig. 122). Extending from the right side of the duodenum along 

 the dorsal and caudal surface of the liver is the hepatic diverticulum. It Kes to 



