78 



HUMAN EMBEYOLOGY. 



folded medially ; the tips of the fingers are free, and the palms rest on the cranial part 

 of the distended abdomen. The thighs and the toes have appeared, and the tail has 

 begun to fuse with the caudal end of the body (Fig. 104). 



At the end of the eighth week, when the embryo becomes a foetus, it has attained a 

 length of about 25 mm. (CR). The auricles project from the sides of the head, the tail 

 has almost disappeared from the surface, and the toes are free from one another. The 

 cervical flexure is now very slight, and although the head is still relatively large, the 

 disproportion between it and the body has begun to decrease (Fig. 105). 



Third Month. The head grows less rapidly, and, though it is still large, it is relatively 

 smaller in proportion to the whole body. The eyelids close, and their margins fuse 



FIG. 104. EMBRYO (CR) greatest length 18'5 mm. 

 Probably between seven and eight weeks old. (From 

 Keibel and Elze's Normaltafeln.} The abdomen 

 is very prominent on account of the rapid increase 

 of the liver. The digits of the hand and foot are 

 distinct but not separated from one another. The 

 margin auricle of the external ear is completed. The 

 eyelids have begun to form. 



FlG. 105. HOMAN FCETUS EIGHT AND A HALF 



WEEKS OLD. (After His. ) 

 GE. Genital eminence ; UC. Umbilical cord. 



together. The neck increases in length. The various parts of the limbs assume their 

 definite proportions, and nails appear on the fingers and toes. The proctodseum is formed 

 and the external generative organs are differentiated, so that the sex can be distinguished 

 on external examination. The skin is a rosy colour, thin and delicate, but more consistent 

 than in the preceding stages. By the end of the third month the total length of the foetus, 

 excluding the legs, is 7 cm. (2| in.), including the legs, 9-10 cm. (3|-4 in.), and it weighs 

 from 100-125 grammes (31-4J oz.). 



Fourth Month. In the fourth month the skin becomes firmer, and fine hairs are 

 developed. The disproportion between the fore- and hind-limbs disappears. If the foetus 

 is born at this period it may live for a few hours. Its total length from vertex to heels 

 is 16-20 cm. (6f-8 in.), from vertex to coccyx 12-13 cm. (4i-5i in.), and it weighs from 

 230-260 grammes (81-94 oz.). 



Fifth Month. The skin becomes firmer, the hairs are more developed, and sebaceous 

 matter appears on the surface of the body. The legs are longer than the arms, and the 

 umbilicus is farther from the pubis. At the end of the month the total length of the 



