852 EMBRYOLOGY 



is then four to five inches (10.1 to 12.7 centimeters) long and weighs 

 about five ounces (141.7 grams). The muscles show contractility; the 

 eyes, mouth and nose are closed; the gall-bladder is just developed; 

 the fontanelles and sutures are wide ; the sex is distinguishable. 



At the fifth month the foetus is nine to twelve inches (22.8 to 30.5 

 centimeters) long and weighs five to nine ounces (141.7 to 255.1 grams). 

 The hairs begin to appear on the head ; the liver begins to secrete bile, 

 and the meconium appears in the intestinal canal; the amnion is in 

 contact with the chorion. 



At the sixth month the foetus is eleven to fourteen inches (27.9 to 

 35.5 centimeters) long and weighs one and a half to two pounds (680 

 to 907 grams). If the foetus is delivered at this time, life may continue 

 for a few moments ; the bones of the head are ossified, but the fonta- 

 nelles and sutures are still wide ; the prepuce has appeared ; the testicles 

 have not descended. 



At the seventh month the foetus is fourteen to fifteen inches (35.5 to 

 38.1 centimeters) long and weighs two to three pounds (907 to 1361 

 grams). The hairs are longer and darker ; the pupillary membrane 

 disappears, undergoing atrophy from the centre to the periphery ; the 

 relative quantity of the amniotic fluid is diminished, and the foetus is 

 not so free in the cavity of the uterus ; the foetus is now viable. 



At the eighth month, the foetus is fifteen to sixteen inches (38.1 to 

 40.9 centimeters) long and weighs three to four pounds (1361 to 1814 

 grams). The eyelids are opened and the cornea is transparent ; the 

 pupillary membrane has disappeared; the left testicle has descended; 

 the umbilicus is at about the middle of the body, the relative size of the 

 lower extremities having increased. 



At the ninth month the foetus is about seventeen inches (43.2 centi- 

 meters long and weighs five to six pounds (2.27 to 2.72 kilograms). Both 

 testicles usually have descended, but the tunica vaginalis still communi- 

 cates with the peritoneal cavity. 



At birth the infant weighs a little more than seven pounds (3.17 

 kilograms), the usual range being four and ten pounds (1.81 and 4.53 

 kilograms), although these limits are sometimes exceeded. 



The position of the foetus in the great majority of cases, excluding 

 abnormal presentations, is with the head downward. In the early 

 months of pregnancy the foetus floats quite freely in the amniotic 

 liquid ; and it. is probable that the natural gravitation of the head and 

 of the upper part of the foetus is the determining cause of the ordinary 

 position in utero. 



The shape of the uterus at full term is ovoid, the lower portion being 

 the narrower. The foetus has the head slightly flexed upon the sternum, 



