LATERAL DISSECTION OF THE VISCERA 



103 



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

 culum (Fox, Thyng). The dorsal diverticula are large and wing-like (Fig. 99), 

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

 Between the ventral diverticula of the third pouch lies the median thyreoid 

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



Eye 



Maxillary process 



Mouth 



Br. arch 3 

 Br. arch 4 



Upper limb bud 



Hepatic diverticulum 



Yolk-sac 



Body-stalk 



Allantois 



Umbilical artery 



Mesonephric duct 



Fronto-nasal process 



Olfactory pit 



Mandibular process 

 Br. arch 2 

 Aortic bulb 



Stomach 



Cephalic loop of intestine 

 Mesonephros 

 Mesonephric duct 

 Caudal loop of intestine 



Lower limb bud 



-Rectum 

 Dorsal aorta and umbilical artery 



FIG. 92. A ventral dissection of a 6 mm. pig embryo. The head has been bent dorsally. Br. arch 2, 

 3 and 4, branchial arches, 2, 3 and 4. 



him just meets the ectoderm, its ventral portion is small, tubular in form and is 

 directed parallel to the esophagus (Fig. 99). 



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 

 the trachea has separated from the esophagus. The trachea at once bifurcates to 

 form the primary bronchi, and the anlages of the lungs. 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 near the cardiac end of the 



