144 



THE HUMAN EMBRYO. 



wide. It has three lateral outgrowths on each side, i, 2, 3, the gill-pouches. In 

 front and near the cephalic end of the notochord there is a small median out- 

 growth, the anlage of the hypophysis, Hy. Toward the neck-bend the pharynx 

 becomes narrower and passes over into the small entodermal tube, from which we 

 can detect the outgrowth, Lu, which represents the commencing formation of the 

 lungs. This narrow tube leads to the space above the yolk-sac, Yk.s. Just 



FIG. 89. HUMAN EMBRYO 4.2 MM. 

 Yks, Yolk-sac. Am, Amnion. All, 

 Body-stalk. (After W, His.) 



Car. 



FIG. 90. RECONSTRUCTION or THE 

 ANATOMY OF THE EMBRYO OF 2.6 

 MM. IN FIGURE 88. 



A, Aortic limb of heart. All, Body-stalk. 

 Ao, Dorsal aorta. Au, Umbilical 

 arteries. Car, Posterior cardinal 

 vein. Jg, Anterior cardinal vein. 

 Om, Omphalo-mesaraic vein, op, 

 Optic, vesicle. ot, Otocyst. Vh, 

 right umbilical vein. (After W. 

 His.) 



where it passes into the yolk-sac the entoderm has formed the rudiment of the 

 liver, Li. Figure 55 gives a view of the anterior wall of the pharynx of another 

 embryo. In front is the large opening of the mouth, M, the oral plate between 

 the mouth-cavity and the entodermal canal having disappeared. This embryo 

 being a little older, the traces of the four gill-clefts can already be seen, and there 

 are four entodermal gill-pouches. The aortic vessels are indicated by dotted lines. 

 The cardiac aorta reaches the pharynx between the bases of the second and third 

 gill-arches, and divides into two branches, one on each side. The anterior branch 



