378 



TEXT-BOOK OF EMBRYOLOGY. 



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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 

 grooves gradually grow deeper, the peritoneum 

 pushing its way, as a flat sac, between the two 

 structures, until the separation is almost complete. 

 There is left, however, an area of attachment 

 between the liver and diaphragm, over which the 

 peritoneum is reflected, the ligamenlum coronarium 

 hepatis. In the medial line there is also left a 

 broad thin lamella which is attached to the dia- 

 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 ligamenlum teres hepatis which is closely related to the 

 umbilical vein (see p. 265). 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 vertebra?. During 

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

 seen in Fig. 336. 



Fig. 336. — Diagram showing the 

 position of the diaphragm in 

 human embryos of different 

 stages. Mall. 



The positions are those shown 

 in embryos of Mall's collection 

 (except KO, which is a 10.2 

 mm. embryo of the His collec- 

 tion) ; XII being an embryo of 

 2.1 mm.; XVIII, of 7 mm.; 

 XIX of 5 mm.; II, of 7 mm.; 

 IX, of 17 mm.; XLIII, of 15 

 mm.; VI, of 24 mm. The 

 numerals on the right indicate 

 segments. 



