506 Till: HUMAN EMBRYO. 



but not nearly so much so as in the earlier stages: the lipa 

 and eyelids are closed, and the helix of the ear is folded down 

 so as to almost close the meatus. The neck is longer than 

 before. The limbs, though small, have acquired their definite 

 shape and proportions ; and nails are present, as thin plates, on 

 both fingers and toes. The integument is slightly firmer than 

 before, but is still very thin, transparent, and rose-coloured. 



Up to this stage a loop of the intestine has been situated in the 

 allantoic stalk, and therefore outside the embryo; but by the end 

 of the third month this loop is withdrawn, and the whole alimen- 

 tary canal, which has increased greatly in length, is from this 

 time situated within the abdominal cavity. 



During the third month, the external genital organs become 

 established. The history of their development will be given in 

 the section dealing with the organs of reproduction. 



9. The Fourth Month. 



At the end of the fourth month the foetus measures 12 to 13 

 cm. in length, from the vertex of the head to the coccyx ; or from 

 16 to 20 cm. if the legs be included. The weight is usually from 

 230 to 260 grammes. 



The skin is of a rosy colour, and is much firmer than before . 

 Short whitish hairs appear on the head, and a slight down on 

 other parts of the body. The eyelids, nostrils, and lips are all 

 closed. The chin, which has hitherto been inconspicuous, begins 

 to become prominent. The legs and arms are of about equal 

 length : and the external sexual characters are iisually well- 

 marked. 



The anus is open, and the duodenum contains meconium of 

 a light greyish-white colour. The umbilicus, or point of origin 

 of the umbilical cord, is low down, close to the pubes. In the 

 skull, the bones are still far from meeting one another, so that the 

 sutures and fontanelles are very wide. The muscles are more 

 fully developed than before, and may give rise to distinct move- 

 ments of the foetus. In abortions at this period the foetus may 

 live for some hours. 



10. The Fifth Month. 



By the end of the fifth month the foetus measures about 

 20 cm. in length; or, if the legs be included, 25 to 27 cm. 

 The average weight is about half a kilogramme. 



