64 



HUMAN ANATOMY. 



progressed that fingers and toes are distinctly indicated, although the fingers only- 

 are imnerfectly separated. The first suggestion of the external genitals appears 

 about the end of the sixth week. At this time the foetus measures about nineteen 

 millimetres. 



During the seventh and eighth weeks the fcetal form of the body and the 

 limbs attain greater perfection, the large head becoming raised from the trunk and the 

 toes, as well as fingers, being now well formed, although the rudiments of the nails 

 do not appear until some time during the third month. At the close of the second 

 month the extra-embryonic protrusion of the intestine through the umbilicus into 

 the umbilical cord reaches its greatest extent. The genito-urinary system is repre- 

 sented by the fully developed Wolfifian body, the vesical dilatation of the allantoic 

 duct, the separation of the cloaca into rectum and genito-urinary passage, the indif- 



FiG. 78. 



Umbilical vesicle. 



TT IT - .,^? '■ 

  f* 



Human embryo of about thirty-five days. X 4. Amnion and chorion cut and turned aside. 



ferent sexual gland, and the undifferentiated external genitals, consisting of the geni- 

 tal eminence and the associated genital folds and genital ridges. The external ear 

 has assumed its characteristic form, and the eyelids appear as low folds encircling the 

 conspicuous eye, in which the pigmentation of the ciliary region is visible. Although 

 the face is well formed, the nose is still flat, the lips but slightly prominent, and the 

 palate not completely closed. The rapid growth of the brain results in the dispro- 

 portionate size of the head, which at this stage almost equals the trunk in bulk. It 

 is to be noted that by the close of the second month the permanent organs are so 

 far advanced that the subsequent growth of the foetus is effected by the further de- 

 velopment of parts already formed and not by the accession of new organs. The 

 beginning of the second month marks the period of greatest relative growth; at 

 the end of this month the foetus measures about thirty millimetres in its longest 

 dimension. 



