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TEXT-BOOK OF EMBRYOLOGY. 



cavity comes to occupy much of the ventral part of the thorax, the pericardium 

 having extensive attachments to the ventral body wall and to the cephalic sur- 

 face of the primary diaphragm (Fig. 330). The diaphragm is much farther 

 forward than in the adult and is broadly attached to the cephalic surface of the 

 liver. The principal changes which bring about the adult conditions are the 

 growth of the lungs, the separation of the diaphragm from the liver, and the 



caudal migration of the diaphragm itself. With 

 the development of the lungs, the pleural cavities 

 necessarily enlarge and push their way ventrally. 

 In so doing they split the pericardium away from 

 the lateral body walls and likewise from the dia- 

 phragm (compare Figs. 334 and 335). Thus the 

 pericardial cavity comes to be confined more and 

 more closely to the medial ventral position. The 

 separation of the liver from the primary diaphragm 

 is caused by changes in the peritoneum which at 

 first covers the caudal, lateral and ventral surfaces 

 of the liver. The cephalic surface of the liver, as 

 stated above, is covered by the primary diaphragm 

 itself. The peritoneum is reflected from the surface 

 of the liver on to the diaphragm, and at the line of 

 reflection a groove appears on each side, extending 

 from the midventral line around as far as the 

 attachment of the liver to the diaphragm. The 

 FIG. 336. Diagram showing the grooves gradually grow deeper, the peritoneum 

 human^e^br^^^F^lerent pushing its way, as a flat sac, between the two 

 stages. Mall. structures, until the separation is almost complete. 



The positions are those shown . 



in embryos of Mall's collection There is left, however, an area of attachment 

 (except KO, which is a 10.2 between the liver and diaphragm, over which the 



mm. embryo of the His collec- m f r 



tion) ; xii being an embryo of peritoneum is reflected, the ligamenlum coronarium 



In the medial line there is also left a 



ix, of 17 mm.; XLin, of 15 broad thin lamella which is attached to the dia- 



mm.; VI, of 24 mm. The 



numerals on the right indicate phragm, the liver and the ventral body wall. This 



is a remnant of the ventral mesentery and forms 



the ligamenlum suspensorium (falciforme) hepatis. In its free caudal edge 

 is embedded the ligamentum teres hepatis which is closely related to the 

 umbilical vein (see p. 261). The diaphragm itself, during its development, 

 migrates from a position in the cervical region, where the septum transversum 

 first appears, to its final position opposite the last thoracic vertebrae. During 

 the migration the plane of direction also changes several times, as may be 

 seen in Fig. 336. 



