DEVELOPMENT OF THE FALLOPIAN' TUBE.
Whatever difference of opinion may exist regarding the origin of the excretory duct of the male generative gland, there appears to be no doubt, that in birds at least the correspond ing part in the female has its commencement in a structure which, as soon as it can be recognised as a distinct tube, is altogether separate from the Wolffian body. This is called after its first observer, tne duct of Midler* (fig. 400. g.).
The mode of origin of this duct has been already partly described in the account v.hich has been given of the formation of the Paro varium (p. 594.). Its development may be most conveniently traced in birds, where it can be easily shown that the oviduct is not a metamorphosis of the excretory duct of the Wolffian body, but may be distinguished lying near it, in the form of a tolerably thick tube ; which at first ends in a closed extremity, but afterwards exhibits a wide orifice. It runs along the outer side of the Wolffian body, while its infundibulum, which is soon distin guishable, extends beyond and is entirely se parate from that body.
The oviducts appear from the first in the form of white cylinders on both sides. They do not grow from below upwards, but are formed in their entire length from the corn mencement ; nor are they- constructed out of a membranous lamina, rolled together, as Meckel supposed ; but are in the beginning solid, and become gradually hollowed out into a tube. In this way also is formed the infun dibular opening of the tube into the abdomi nal cavity.
Two oviducts exist originally in all birds, but as in this class the right ovary shrinks and disappears, so the right oviduct becomes lost, by gradually contracting and shortening from above downwards. f In mammals, before the distinction of sex becomes apparent internally, there is seen, running along the Wolffian body of each side in every embryo, a duct, which, according to Miller, may represent either a vas deferens, or an oviduct. These ducts lie upon opposite sides of the germ glands, which may become afterwards testis or ovary.
Soon afterwards the internal organs begin to exhibit a distinction of sex. This is indi
cated in the future male by the duet, laid' runs along the outer side of the Wolffian body, sending off a white granular projection, extending towards the testis, which is met by a similar projection, given off' by the upper end of the testis, and these two by their union forni the rudiments of the epididyrnis. So that in the male mammal a new connexion is established between the duct, which after wards becomes vas deferens, and the testis, without any agency from the Wolffian body, but through the development of new material.
In the female these projections are wanting, both from the excretory duct and from the ovary. The latter remains attached only to the Wolffian body by a siniple fold. The up per end of the duct, which runs over the Wolffian body, projects somewhat beyond that body inferiorly, and terminates here in a glo bular swelling, in which an aperture is formed at a later period.
As the Wolffian body becomes atrophied the portion of the duct which takes its course over it, and which was previously straight, beg,ins to be tortuous in the male, while in the female it remains straight, but becomes wider. Out of corresponding portions of the duct are formed, in the male, the head of the epi didymis, and in the female the infundibular end of the tube, while the inferior free por tion of the duct, after it has quitted the Wolffian body becomes converted, in the niale, into the vas deferens, becoming at the same time more and more elongated ; but in the fernale the corresponding portion of the duct is transformed into the inferior division of the tube, or into the cornu of the uterus.* In this sta,ge of its development the inci pient Fallopian tube is only bevinning to be recognisable. It circumscribesbthe diminish ing Wolffian body on its outer side in the form of a bow. Above the superior opening extends beyond that body, while below the short free portion becomes conjoined with that of the opposite side to form a single tube. These ducts have throughout the same breadth up to their union with each other.