THE ANATOMY OF A 4.2 MM. HUMAN EMBRYO 



91 



the floor of the pharynx, is developed the tuberculum impar which may form a 

 portion of the anterior part of the tongue. Posterior to this unpaired anlage of 

 the tongue there grows out ventrally the anlage of the thyreoid gland. From 

 the caudal end of the trachea have appeared ventrally the lung buds. The 

 trachea is still largely a groove in the ventral wall of the pharynx and esophagus. 

 Caudal to the lungs a slight dilation of the digestive tube indicates the position 



Moulh cavity 



Pharyngeal 

 pouches /-4- 



trachea 

 Lung bud 



Hepatic diverticulum 

 Ventral pancreas 



Mesonephric tubule 

 With glomerulus 



Hind-gut 

 Allantois 



Tail-gut 



Thyreoid anlage 



Esophagus 



Otomach 



Dorsal pancreas 

 YolK-stalK 



Mesonephros 

 Mesonephric duct 



Cloaca. 



FIG. 82. — Diagrammatic ventral view of pharynx, digestive tube and mesonephroi of a 4-5 mm. 

 embryo (based on reconstructions by Grosser and His). The liver and yolk-sac are cut away. The 

 tubules of the right mesonephros are shown diagrammatically. 



of the stomach. The liver diverticulum has grown out from the fore-gut into 

 the ventral mesentery cranial to the wall of the yolk-stalk. It is much larger 

 than in the fifty-hour chick, where we saw its paired anlage cranial to the 

 fovea cardiaca, and is separated from the heart by the septum transversum. The , 

 small intestine between the liver and yolk-stalk is short and broad. In later 

 stages it becomes enormously elongated as compared with the rest of the diges- 

 tive tube. The yolk-stalk is still broad and wide. The region of its attachment 



