

FORM OF THE EMBRYO AT DIFFERENT STAGES OF ITS GROWTH 77 



are directed forward and the palate is not completely developed. The eyelids are present in the 

 shape of folds above and below the eye, and 'the different parts of the auricula are distinguish- 

 able. By the end of the second month the fetus measures from 28 to 30 mm. in length (Fig. 63). 



Third Month. The head is extended and the neck is lengthened. The eyelids meet and fuse, 

 remaining closed until the end of the sixth month. The limbs are well-developed and nails appear 

 on the digits. The external generative organs are so far differentiated that it is possible to dis- 

 tinguish the sex. By the end of this month the length of the fetus is about 7 cm., but if the legs 

 be included it is from 9 to 10 cm. 



Fourth Month. The loop of gut which projected into the umbilical cord is withdrawn within 

 the fetus. The hairs begin to make their appearance. There is a general increase in size so that 

 by the end of the fourth month the fetus is from 12 to 13 cm. in length, but if the legs be included 

 it is from 16 to 20 cm. 



Fifth Month. It is during this month that the first movements of the fetus are usually ob- 

 served The eruption of hair on the head commences, and the vernix caseosa begins to be deposited. 

 By the end of this month the total length of the fetus, including the legs, is from 25 to 27 cm 



Sixth Month. The body is covered by fine hairs (lanugo} and the deposit of vernix caseosa 

 is considerable. The papillae of the skin are developed and the free border of the nail projects 

 from the corium of the dermis. Measured from vertex to heels, the total length of the fetus 

 at the end of this month is from 30 to 32 cm. 



Seventh Month. The pupillary membrane atrophies and the eyelids are open. The testis 

 descends with the vaginal sac of the peritoneum. From vertex to heels the total length at the 

 end of the seventh month is from 35 to 36 cm. The weight is a little over three pounds. 



Eighth Month. The skin assumes a pink color and is now entirely coated with vernix caseosa, 

 and the lanugo begins to disappear. Subcutaneous fat has been developed to a considerable 

 extent, and the fetus presents a plump appearance. The total length, i. e., from head to heels, 

 at the end of the eighth month is about 40 cm., and the weight varies between four and one-half 

 and five and one-half pounds. 



Ninth Month. The lanugo has largely disappeared from the trunk. The umbilicus is almost 

 in the middle of the body and the testes are in the scrotum. At full time the fetus weighs from 

 six and one-half to eight pounds, and measures from head to heels about 50 cm. 





BIBLIOGRAPHY. 



BROMAN: Normale und abnorme Entwicklung des Menschen, 1911. 



BRYCE, TEACHER and KERR: Contributions to the Study of the Early Development and 

 Imbedding of the Human Ovum, 1908. 



HERTWIG, O.: Handbuch der Vergleichenden und Experimentellen Entwicklungslehre der 

 Wirbeltiere, 1906. 



His, W. : Anatomie menschlicher Embryonen, 1880-1885. 



HOCHSTETTER, F. : Bilder der ausseren Koperform einiger menschlicher Embryonen aus den 

 beiden ersten Monaten der Entwicklung, 1907. 



KEIBEL and ELZE: Normentafel zur Entwicklungsgeschichte des Menschen, 1908. 



KEIBEL and MALL: Manual of Human Embryology, 1910-1912. 



KOLLMANN, J.: Handatlas der Entwicklungsgeschichte des Menschen, 1907. 



KOLLMANX, J.: Lehrbuch der Entwicklungsgeschichte des Menschen, 1898. 



MALL: Contribution to the Study of the Pathology of the Human Embryo, Jour, of Morph., 

 1908. See also contributions to Embryology of the Carnegie Institution of Washington. 



MALL: Development of the Human Ccelom, Jour, of Morph., 1897. 



PETERS, H.: Ueber die Einbettung des menschlichen Eies und das friiheste bisher bekannte 

 menschliche Placentationsstadium, 1899. 



