342 



THE EVOLUTION OF MAN. 



the axis of the solid cell-cords ; they all discharge into the 

 two primitive main gall or biliary ducts, which originate 

 from the base of the two original protuberances of the 

 intestine. In Man, and in many other Vertebrates, these 

 two ducts afterwards unite, and form one simple gall-duct, 

 which discharges into the ascending portion of the gall- 

 intestine. The gall bladder originates as a hollow pro- 

 tuberance of the right primitive liver duct. The growth 

 of the liver is at first exceedingly rapid; in the human 

 embryo, even in the second month, it attains such dimen- 

 sions that during the third month it occupies by far the 

 largest part of the body-cavity (Fig. 288). At first, both 



FIG. 288. Chest and abdominal viscera of a 

 human embryo of twelve weeks, in natural size. 

 (After Koelliker.) The head is omitted ; the chest 

 and abdominal walls removed. The greater part 

 of the abdominal cavity is occupied by the liver, 

 from an opening in the centre of which the blind- 

 intestine (caecum, v), with the worm appendage,, 

 protrudes. Above the diaphragm the heart is 

 visible in the centre, with the small lungs on the 

 right and left. 



halves are equally well developed ; afterwards the left half 

 lies considerably behind the right. In consequence of the 

 asymmetrical development and alteration in the position of 

 the stomach and other abdominal viscera, the whole of the 

 liver is eventually forced o^er on to the right side. Although 

 the growth of the liver is, afterwards, not so excessive, even 

 at the end of gestation, it is comparatively much larger in 

 the embryo than in the adult. In the latter, its weight 



