STAGE OP^ THE FCETUS. 



65 



The third month is characterized by greater perfection of the external form, 

 the rounded head is raised from the trunk so that a distinct neck appears, while the 

 thorax and abdomen are less prominent ; the limbs, which are well developed with 

 completed differentiation of the fingers and toes, provided with imperfect nails, now 

 assume the characteristic foetal attitude. The eyelids become united by the tenth 

 week, remaining- closed until the end of the seventh month. The cloacal opening 

 becomes differentiated during the ninth and tenth weeks into the genito-urinary and 



Fig. 79. 



Umbilical cord 



Umbilical 

 stalk 



Allantoic 

 vessels 



Umbilical vesicle . 



Human foetus of aoout eight weeks. X 3%. Amnion has been cut and reflected, but still covers the umbilical vesicle 



and its stalk. 



the anal orifice, while during the eleventh and twelfth weeks the external genital 

 organs acquire the distinguishing peculiarities of a definite sex. The greatest length 

 of the foetus, measured in its natural position and excluding the limbs, at the 

 end of the third mOnth, is about eighty millimetres ; its weight approximates twenty 

 grammes. 



The fourth month witnesses augmented growth in the foetus, which, how- 

 ever, resembles in its general appearance the foetus of the preceding month. The 



