90 



GENERAL HISTORY OF DEVELOPMENT 



give rise, while the cleft itself becomes the concha and part of the external auditor 

 meatus. By the end of the month the auricle is so far developed that the adult 

 parts can be readily recognised. The transformations may be readily understood 

 from the study of the accompanying series of sketches copied from His, which 

 show these parts in gradually advancing stages in the human embryo (fig. 127). 



decMua 



decidua capsularis 



FIG 128. PREGNANT UTERUS AT THE BEGINNING or THE THIRD MONTH. 



The uterus has been opened up ; a window has been made in the decidua capsularis, and also in the 

 amnion, to show the foetus in situ. A large plug of mucus occupies the canal of the cervix. The 

 bristles indicate the openings of the Fallopian tubes. The cut edge of the decidua capsularis shows 

 the villi of the chorion laeve. (From a preparation by Dr. J. H. Teacher.) 



Limbs. In the fifth week the limb-buds considerably enlarge, and show a 

 subdivision into two, then into three, segments (fig. 121). The terminal segment 

 which forms the hand or foot is broadened out and differentiated into a thicker 

 basal, and a thinner marginal portion. At the base of the thin marginal segment 

 the rudiments of the fingers and toes appear as small tubercles, which soon reach 

 the free margin. During the sixth week the limbs increase in size, the elbow and 





