THE ANATOMY OF A SIX MM. PIG EMBRYO 



95 



Laterally and ventrally between the arches are the four paired outpocke tings of 

 the pharyngeal pouches. The pouches have each a dorsal and ventral divertic- 

 ulum (Fox, Thyng). The dorsal diverticula are large and wing-like (Fig. 104); 

 they meet the ectoderm of the gill clefts and fuse with it to form the closing plates. 

 Between the ventral diverticula of the third pair of pouches lies the median thy- 

 reoid anlage. The fourth pouch is smaller than the others. Its dorsal diverticu- 



Eye 

 Maxillary process 



MoHlh 



Branchial arch j 

 Branchial arcli 4 



Upper limb bud 



Hepatic diverticttlum 



Yolk sac 



Body stalk 



AUatitciis 



Umbilical artery 



Mesonephric duel 



Pronto-nasal process 



Olfactory pit 



Mandibular process 

 Branchial arch 2 

 Aortic bulb 



Trachea 

 Lung bud 



Stomach 



Cephalic loop of intestine 

 Mesonepkros 

 Mesonephric duct 

 Caudal loop of intestine 



Lower limb bud 



\ — -Rectum 



Dorsal aorta and umbilical artery 



Fig. 97. — ^Ventral dissection of a 6 mm. pig embryo. X 14. The head has been bent dorsally. 



lum Just meets the ectoderm; its ventral portion is small, tubular in form, and is 

 directed parallel to the esophagus (Fig. 104). 



The groove on the floor of the pharynx caudal to the epiglottis is continu- 

 ous with the tracheal groove. More caudally, opposite the atrium of the heart, 

 Xht .trachea has separated from the esophagus (Fig. 96). The trachea at once 

 bifurcates to form the primary bronchi and the anlages of the lungs (Fig. 97). 

 The lungs consist merely of the dilated ends of the bronchi surrounded by a layer 

 of splanchnic mesoderm. They bud out laterally on each side of the esophagus 



