4:50 GENERATION. 



At the seventh month, the foetus is from fourteen to 

 fifteen inches long, and weighs from two to three pounds. 

 The hairs are longer and darker ; the pupillary membrane 

 disappears, undergoing atrophy from the centre to the periph- 

 ery ; the relative quantity of the amniotic fluid is dimin- 

 ished, 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 from fifteen to sixteen 

 inches long, and weighs from three to four pounds. The 

 eyelids are opened and the cornea is transparent ; the pupil- 

 lary membrane has disappeared ; the left testicle has de- 

 scended ; 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 

 long, and weighs from five to six pounds. Both testicles 

 have usually descended, but the tunica vaginalis still com- 

 municates with the peritoneal cavity. 



At birth, the infant weighs a little more than seven 

 pounds, the usual range being from four to ten pounds, 

 though these limits are sometimes exceeded. 



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

 excluding abnormal presentations, is with the head down- 

 ward ; and why this is the usual and the normal position, is a 

 question which has been the subject of much discussion. As 

 we have just seen, in the early stages of pregnancy, the foetus 

 floats quite freely in the amniotic fluid. Upon this point, Dr. 

 Matthews Duncan has made the following interesting ex- 

 periments : Securing the limbs of the foetus in the natural 

 position which it assumes in utero, by means of threads, and 

 immersing it in a solution of salt of nearly its own specific 

 gravity, he found that it naturally gravitated to nearly the 

 normal position, with the head downward. 1 It is probable, 

 judging from these observations, that the natural gravitation 

 of the head and of the upper part of the foetus is the deter- 

 mining cause of the ordinary position in utero. 



1 J. MATTHEWS DUNCAN, Researches in Obstetrics, New York, 1868, p. 27. 



