434 MALL. [Vor. XII. 
space between it and the chorion, the extraembryonic coelom 
(compare with Fig. 26). Within it hangs this large umbilical 
vesicle, the lumen of which no longer connects with the ali- 
mentary canal. The separation is now complete. Around 
the stem of the vesicle the extraembryonic coelom communi- 
cates freely with the body cavity, as shown in Fig. 30. This 
figure is from a reconstruction, and shows the general extent 
of the body cavity within the embryo. It encircles the heart, 
and then extends to the lungs and over them and to the stomach, 
over the intestines, and out into the cord. A cast of the 
whole cavity is also given, showing the slit 
on the dorsal side for the mesentery of 
the intestine, and the grooves on either 
side of this for the Wolffian bodies. There 
are also grooves in the cast for the veins, 
and the place where the Cuvierian duct 
enters the heart is marked VY. The sagit- 
tal section of the peritoneal cavity is given 
in Fig. 32. The striated line indicates 
where the cavity crosses the median line 
Fic. 32.—Outline of Coelom of the body, while the other lines outline 
in Embryo No. Lin Sagittal the cavity beyond. /. outlines the lesser 
Section. The striated line 
indicates that the coelom peritoneal cavity. Figs. 33-39 give the 
crosses the median line. P, . j 
pericardial spaces /, pleural. €Xtent of the peritoneal cavity in ‘different 
Pai ty of lesser Hortions of the embryo, as indicated by 
the lines'in) Fis. 30; 
It is not difficult now to imagine the body cavity of embryo 
XII converted into the one just described. In that embryo the 
heart is high in the neck on the oval and dorsal side of the 
septum transversum. In this embryo it is on the ventral and 
oral side of the septum transversum, but still above the eighth 
cervical nerve. The septum transversum has already received 
its nerve supply from the fourth cervical nerve, as pointed out 
in the early part of the century by von Bear. This movement 
of the septum transversum is accompanied by a movement of 
all the other organs on their way into the thorax and abdomen 
of the future individual. In the rotation the Cuvierian duct 
acts much as the fixed point about which the coelom is bent. 

