396 EMBRYOLOGY. 



and sch), as THIERSCH and K^LLIKER have shown for Mammals, and 

 as DOHRN and TOURNEUX ET LEGAY afterwards showed for Man. 

 Their formation is accomplished by a process of fusion, which in 

 Man is effected in the second month. When the Miillerijiii duets 

 {fig. 228 mg) are closely pressed together, the partition between them 

 becomes thin and breaks through at first in the middle of the genital 

 cord. Thus there is developed out of them by an extension of this 

 process a single sac (the sinus genitalis), which is also established in 

 the male as a rudimentary organ, the previously mentioned sinus 

 prostaticus or uterus masculinus (fig. 222 um). In woman it begins 

 to be differentiated in the sixth month into uterus and vagina. The 

 upper portion, which receives the oviducts, acquires very thick, 

 muscular walls and a narrow lumen, and is limited below by a re- 

 entering ring-like ridge that becomes the vaginal portion [of the 

 uterus] from the lower portion, the vagina, which remains spacious 

 and possesses a thinner wall. 



Similarly to the testis, the ovaries also have to pass through a con- 

 siderable change in position : the descensus ovariorum (fig. 225 ei', t'), 

 which corresponds to the descent of the testes. In the third month 

 of embryonic life, at the time when the primitive kidney begins to 

 disappear, the ovaries move from the region of the lumbar vertebrae 

 down into the false pelvis, where they are found medianwards from 

 the musculus psoas. Probably the above -described inguinal ligament 

 of the primitive kidney (fig. 225 rm), which is not wanting in the 

 female, participates in the change of position in this case also. As 

 WIEGER has recently shown, the ligament is differentiated into three 

 distinct regions by the fact that it acquires a firm union with the 

 Miillerian ducts at the place where they meet to form the sexual 

 cord. The uppermost region becomes a strand of non-striate muscle- 

 fibres, which, arising from the parovarium, is imbedded in the hilus 

 of the ovary. This is continuous with the second region, or the 

 ligamentum ovarii (lo') t and the latter with the round ligament (rm) 

 (ligamentum teres uteri). JThe_round ligament, produced from the 

 third and most developed region of the inguinal ligament, extends 

 from the upper end of the genital cord to the inguinal region. Here 

 there is usually, as in the male, a small evagination of the peritoneum, 

 the processus vaginalis peritonei, which occasionally persists even in 

 the adult as the diverticulum Nuckii, and then may likewise be the 

 cause of the formation of an inguinal hernia in the female. At this 

 place the round ligament passes through the wall of the abdomen 

 and ends in the external skin of the labia majora. 



