82 



THE FETAL MEMBRANES AND EARLY HUMAN EMBRYOS 



pouches (Fig. 87). Later a fifth pair of pouches is developed (Fig. 168). The 

 four pairs of pharyngeal pouches are important as they form respectively the 

 following adult structures: (1) the auditory tubes; (2) the palatine tonsils; (3) the 

 thymus anlages; (4) the parathyreoids or epithelial bodies. Between the pharyn- 

 geal pouches are the five branchial arches in which are developed five pairs of 

 aortic arches. Between the bases of the first and second branchial arches, on 



Mouth cavity 

 Thyreoid anlage 



Pharyngeal pouches l-J-t 



Esophagus 



Stomach 



Hepatic diverticuUim 

 Ventral paiinoas 



Mesonephric tubide with glomerulus 

 Hind-'^iil 



Allanlois 



Dorsal pancreas 

 oik stalk 



Mcsonephros 

 Mesonephric duct 



Cloaca 



Tail gill 



Fig. 87. — Diagrammatic ventral view of pharynx, digestive tube, and mesonephroi of a 4-5 mm. 

 embryo (based on reconstructions by Grosser and His). X about 30. The liver and yolk sac are cut 

 away. The tubules of the right mesonephros are shown diagrammatically. . 



the floor of the pharynx, is developed the tuberculum impar which perhaps forms 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 

 (Fig. 86). Caudal to the lungs a slight dilation of the digestive tube indicates the 



The liver diverticulum has grown out from the fore-gut 



position of the stomach. 



