THE SECOND MONTH. 



505 



fore-limb, which is still the larger of the two, has the charac- 

 teristic shape of the huinan arm. The thumb is clearly marked 

 off from the fingers, and the deltoid swelling at the shoulder is 

 already prominent. The leg is smaller than the arm, and is so 

 directed that the soles of the feet are apposed. 



The neck is well marked, though short. The ventral wall 

 of the body is completely formed. The umbilical cord, which 

 attaches the embryo to the placenta, is about 8 or 10 mm. long : 

 it is as a rule straight, but may be slightly twisted on itself. 

 It is formed by the allaiitoic stalk and yolk-stalk, bound together 



FIG. 213. 



FIG. 214. 



FIG. 213. Head of a Human Embryo at the end of the seventh week. HM, 



external auditory meatus. (From His.) x 5. 



FIG. 214. Head of a Human Embryo at the end of the second month. (From 



His.) x 3. 



by the amnion, and it still contains at its base a loop of the 

 intestine. 



From the end of the second month, when the definite human 

 form is established, up to the time of birth, it is customary to use 

 the term foetus in place of embryo. 



8. The Third Month. 



At the end of the third month the foetus measures about 

 7 cm. in length, or 9 to 10 cm. if the legs be included, and weighs 

 from 100 to 125 grammes. 



The head is still very large relatively to the rest of the body, 



