408 OUTLINES OF CHORDATE DEVELOPMENT 



and the tail has reached nearly to the condition of its greatest 

 development. 



The further development of the general bodily topography 

 may be sketched very briefly with the aid of the accompanying 

 figures (Figs. 168, 169, 170). During the latter part of the 

 second month (Fig. 169) the head continues to be elevated 

 rapidly, and the body to straighten. The head is now at its 



FIG. 168. Human embryo of 14.5 mm. (thirty-six days) showing thick um- 

 bilical cord, and yolk-sac at the end of the slender yolk stalk. After Minot. 

 X 4.3. For description see text. 



greatest relative size, constituting about 45 per cent, of the 

 total weight of the embryo (Jackson). The pinna of the ear 

 is formed from elevations of the first and second visceral arches 

 around the external auditory meatus. The rudiments of the 

 eye are fully established and the eyelids are formed. The 

 ventral body wall still remains protuberant. The proximal 

 end of the umbilical cord becomes considerably expanded, and 

 into its extra-embryonic coelomic cavity extend several coils of 

 the embryonic intestine and even a portion of the liver. This 

 characteristic extension of the intestine (intestinal hernia) 



