Embryology. 25 



bodies, or primitive kidney ducts, puts forth a branch near the point of 

 union with the intestine (or cloaca). This branch runs forward parallel 

 with the kidne} r duct and terminates near the egg or germ gland. It is 

 called the miillerian duct. This mullerian duct and the wolffian, or prim- 

 itive kidney duct, are to become the seed ducts to convey the germ cells 

 from the sexual gland. 



The sex at this time is not determined, or rather the embryo belongs 

 to both sexes, and the germ gland is, no doubt, a rudimentary herm- 

 aphrodite gland. When the sex is determined, (which in the human em- 

 bryo occurs from the 7th to 10th week) if it is a male the testis is de- 

 veloped at the upward or forward end of the wolffian ducts, the lower 

 ends remaining as sperm ducts, while the whole of the mullerian ducts 

 disappear except a useless rudimentary remnant which receives the 

 name, male uterus. 



If the embryo is a female, the ovaries develop from the upper or for- 

 ward end of the mullerian duct, while the lower end of the mullerian 

 duct widens into a pouch which becomes the uterus. At this stage of 

 the development the female embryo has two uteri, one on each side. 

 Later, the lower ends of the two uteri unite into one, and those parts of 

 the ducts leading from its corners to the ovaries, become the fallopian 

 tubes. The wolffian duct, in the female, is reduced to a useless and 

 f unctionless rudiment called the parovarium or supplementary ovary. 



The position of these organs changes during the development of the 

 embryo. From being in the neighborhood of the kidneys they gradu- 

 ally work their way towards the posterior end of the body. The ovaries- 

 of the human female finally stop at or in the small pelvis. The male 

 testes, however, go still further, and passing through the pelvis and the 

 groin canal, bring up in the fold of the outer skin, called the scrotum, 

 quite outside of the body; the scrotum itself consisting of the same 

 parts which in the female become the greater lips of the pudendum. 



At the front end of the body, at an early period, a pair of small 

 grooves are formed on the under or front side of the head. These are 

 called the "olfactory grooves." They are simply indentations of the 

 outer skin layer and do not, at first, at all communicate with the internal 

 cavity of the body. Just below these is a like indentation in the outer 

 skin layer, which constantly deepens toward the forward end of the in- 

 testinal cavity, until it at last joins and becomes continuous with it. 

 Thus the mouth and nostrils are formed by andlineft with the outer skin 

 layer. 



Next trace the development of the osseous system. 



The notochord, which is the first rudiment of the backbone as already 

 stated, is separated from the skin fibrous layer at a very early period, as 



