DEVELOPMENT OP THE EMBRYO. 1003 



Human embryo, the rudiments of the sexual organs whether testes or ovaria, 

 first present themselves soon after the kidneys make their appearance, that 

 is, towards the end of the 7th week. They are at first much prolonged, and 

 seem to consist of a kind of soft, homogeneous blastema, in which the structure 

 characteristic of each subsequently develops itself. The Testis gradually as- 

 sumes its permanent form ; the epididymis appears in the tenth week ; and the 

 gubernaculum (a membranous process from the filamentous tissue of the scrotum, 

 analogous to the round ligament arising from the labiuni and attached to the 

 ovary of the female), which is originally attached to the vas deferens, gradually 

 fixes itself to the lower end of the testis or epididymis. The Testes begin to 

 descend at about the middle period of pregnancy ; at the seventh month they 

 reach the inner ring; in the eighth they enter the passage ; and 'in the ninth 

 they usually descend into the scrotum. The cause of this descent is not very 

 clear : it can scarcely be due merely, as some have supposed, to the contraction 

 of the gubernaculum ; since that does not contain any fibrous structure, until 

 after the lowering of the testes has commenced. It is well known that the testes 

 are not always found in the scrotum at the time of birth, even at the full period. 

 Upon an examination of 97 new-born infants, Wrisberg found both testes in 

 the scrotum in 67, one or both in the canal in 17, in 8 one testis in the abdo- 

 men, and in 3 both testes within the cavity. Sometimes one or both testes re- 

 main in the abdomen during the whole of life ; but this circumstance does not 

 seem to impair their function. This condition is natural, indeed, in the ram. 

 The Ovary undergoes much less alteration, either in its intimate structure, or 

 in its position. The efferent canal of the genital apparatus, which in the male 

 forms a continuous connection with the tubular structure of the testes, remains 

 detached from the ovary in the female, having a free terminal aperture, and 

 thus constituting the Fallopian tube. These tubes are at first distinct on the 

 two sides, but they gradually coalesce higher and higher up ;* and it is by an 

 increased development of this coalesced portion, that the Uterus is formed, the 

 homologue of which in the male seems to be the (so called) Vesicula prostatica, 

 or "sinus pocularis," which is sometimes developed to a considerable size, and 

 the relation of which to the orifices of the vasa deferentia is then seen to be 

 essentially the same as that of the female uterus to the Fallopian tubes. 3 



1009. The history of the development of the External Organs of Generation 

 in the two sexes presents matter of great interest, from the light which is 

 thrown by a knowledge of it upon the malformations of these organs, which are 

 among the most common of all departures from the normal type of Human 

 organization. Not only is the distinction of sexes altogether wanting at first ; 

 but the conformation of the external parts of the apparatus is originally the 

 same in Man and the higher Mammalia, as it permanently is in the Oviparous 

 Vertebrata* For, about the 5th or 6th week of embryonic life, the opening of 

 a cloaca may be seen externally, which receives the termination of the intestinal 

 canal, the ureters, and the efferent ducts of the sexual organs j but at the 10th 

 or llth week, the anal aperture is separated from that of the genito-urinary 

 canal or "uro-genital sinus," by the development of a transverse band; and the 

 uro-genital sinus itself is gradually separated, by a process of division extending 

 from before backwards or from above downwards, into a " pars urinaria" and a 

 "pars genitalis," the former of which, extending towards the urachus, is converted 

 into the urinary bladder. A partial representation of this phase of development 



1 For a sketch of those different conditions presented by the Uterus in the several orders 

 of the Mammalian class, which depend upon the degree of this coalescence, see the Author's 

 "Princ. of Phys., Gen. and Comp.," 326, aa, Am. Ed. 



2 See Prof. E. Weber's "Zusatze zur Lehre vom Baue undden Verrichtungen der Ge- 

 schlechtsorgane," Leipzig, 1846. 



