THE ANATOMY OF TEN TO TWELVE MM. PIG EMBRYOS 



121 



Trachea and Lungs. Caudal to the fourth pharyngeal pouches, the 

 esophagus 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 trachea! 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 second- 

 ary bronchial buds arise from the primary bronchus of each lung, and 

 form the anlages of the symmetrical lobes of each lung. 



Lateral nasal process 

 Lacrimal groove 



Maxillary process 

 Mandibular process 



Cervical sinus 

 Trachea 



Trackeal lung bud 



Upper limb bud 



Septum Iranstiersum 



Hepatic diverticiilum 



Yolk sac 



Yolk stalk 



Allantois 

 R. umbilical artery 



Lower limb bud 



Mesonepkric duct 



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 



Melanephros 



Spinal cord 

 Rectum 

 FIG. 1 24. 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 diver- 

 ticulum (Lewis). The pyloric end of the stomach has rotated more to the 

 right, where it opens into the duodenum, from which division of the intes- 

 tine the liver 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 



