of Human Monstrosity. 239 



at the whole circuit of the embryo, which now resembles an invert- 

 ed boat: so that the serous portion of the germinative membrane 

 seems to project over the dorsal surface of the embryo, in all 

 directions, forming a duplicative which surrounds an oval space. 

 The laminae of the duplicative continually grow, and advance 

 towards the centre of this space. This point they soon attain, and 

 then coalesce; and thus is the continuous membrane of the amnion 

 formed: a serous sac which contains the embryo, and which is 

 incomplete only at that part where the ventral plates have not 

 yet coalesced, and which is the navel in mammalia, and the 

 point of communication between the yolk and the abdominal 

 cavity in other creatures. 



The mucous portion of the blastoderma covers the interior, ... 

 abdominal surface of the embryo next its spine, this disposition 

 being- a necessary consequence of the early development of its 

 body on the inferior surface of the serous portion. From this 

 region it spreads itself over the yolk, between it, and the continu- 

 ally spreading- vascular layer. The yolk thus covered, by mucous 

 and vascular membranes, forms the umbilical vesicle of mamma- 

 lia. It is at this moment in the place of the intestines. As the 

 contents of the bag- become diminished by absorption on the part 

 of the embryo, cylindrical portions of it are folded in by the 

 ventral bands coalescing from before backwards, and from behind 

 forwards, the process first beginning towards the head. These 

 cylindrical portions thus form blind diverticula, which adhere 

 closely to the spine at the ends next the head and tail, and more 

 loosely in the intermediate region, where they open into the um- 

 bilical vesicle. As more and more of the vesicle is drawn in 

 and enclosed, the length of the upper and lower bowel encreases : 

 and the ventral plates closing more and more, the passage between 



