608 GENERATION AND DEVELOPMENT. 



trunks for the conveyance of the blood to the heart. The 

 inner portion of the cones forms the cellular structure of the 

 organ into which the bloodvessels extend, and in which they 



FIG. 242. 



Rudiments of the liver on th ' intestine of a chick at the fifth day of incubation, 

 o, heart; b, intestine ; c, diverticulura of the intestine on which the liver (d) is de- 

 veloped; e, part of the mucous layer of the germinal membrane. 



are, with the ducts, gradually developed. The gall-bladder is 

 developed as a diverticulum from the hepatic duct. 



Development of the Respiratory Apparatus. 



The lungs, at their first development, appear as small tuber- 

 cles, or diverticula from the abdominal surface of the oesoph- 



FIG. 243. 

 A B C 



I 



u 



Illustrating the development of the respiratory organs. A, is the oesophagus of a 

 chick on the fourth day of incubation, with the rudiments of the trachea on the 

 lung of the left side, viewed laterally: 1, the inferior wall of the resophagus; 2, the 

 upper wall of the same tube; 3, the rudimentary lung; 4, the stomach. B, is the 

 same object seen from below, so that both lungs are visible, c, shows the tongue and 

 respiratory organs of the embryo of a horse: 1, the tongue; 2, the larynx; 3, the 

 trachea; 4, the lungs viewed from the upper side. (After Rathke.) 



agus. They are united at the anterior part of their circum- 

 ference ; and here a pedicle is formed which becomes elongated 

 into the trachea (see Fig. 243, A, B). Soon afterwards, the 



