1140 UROGENITAL SYSTEM. 
The Wolffian duct serves as the canal or duct for the primitive secretory organ of the 
embryo. It does not persist as such in the adult, yet the adult of both sexes retains 
structures which have their origin in the Wolfhan duct. These adult structures may be 
in a rudimentary or in a functional condition, and the functions performed by them may — 
have changed during the course of development. In the male the canal of the epididymis, 
the vas deferens, and the common ejaculatory duct, are to be looked upon as directly 
developed from the Wolfhian duct of the embryo; while in the female the longitudinal 
duct of the parovarium and the hydatids of Morgagni are rudimentary structures having 
a like origin. Further, the ureter and its pelvis, together with the complicated system of 
Fra. 780.—DEVELOPMENT OF THE BLADDER, URETER, AND KIDNEY. From the models by Professor Keibel. 
A, Caudal portion of an embryo of 15 to 18 days old. The cloaca is relatively very large, and is not yet joined 
by the Wolffian ducts ; an indication is present of the separation of the cloaca into dorsal or rectal, and 
ventral or urogenital, subdivisions. 
B. The cloaca of an older embryo—25 to 27 days old. The subdivision of the cloaca is more clearly marked. 
The Wolffian duct is seen joining the anterior subdivision, and from the lower part of the duct an out- 
growth is present, which gives origin to the ureter and the kidney. 
C, Still older stage (36 to 37 days old). The ureter has acquired a separate opening into the developing bladder, 
which is placed upon the same level as that of the Wolffian duct. The kidney is much more advanced, 
and the rectum is becoming separated from the urogenital canal. 
D. Female embryo 84 to 9 weeks old. The openings of the ureter and genital ducts have become separated by 
a considerable interval. The urogenital canal and rectum have acquired separate openings. 
1, Spinal cord ; 2, Notochord ; 3, Pubic symphysis ; 4, Cloacal membrane, forming the floor of the ectodermal 
cloacal fossa ; 5, Allantoie canal; 6, Rectum, or rectal subdivision of cloaca ; 7, Urogenital subdivision 
of cloaca; 8, Bladder; 9, Urogenital canal; 10, Wolftian duct ; 11, Ureter (or ureter and developing 
kidney) ; 12, Miillerian duct ; 13, Genital eminence. 
kidney tubules which open into it, arise in both sexes as an outgrowth from the Wolffian 
duct. In the male the vesicula seminalis also arises as a diverticulum of the Wolfhan 
duct (Fig. 781). 
The primitive excretory organ—mesonephros—develops in connexion with the 
anterior part of the Wolffian duct (p. 30), and is during the early life of the embryo a 
most important structure. With the development of the permanent kidney the meso- 
nephros atrophies, yet some of its tubules persist in the adult. The vasa efferentia, the 
ductuli aberrantes, and the rudimentary paradidymis (organ of Giraldés) in the male, and 
the rudimentary tubules of the parovarium (epoophoron) and of the paroophoron in the 
female, are structures which owe their origin to tubules of the mesonephros. 
Soon after the formation of the Wolffian ducts two other longitudinally-disposed canals, 
called the Miillerian ducts, are developed. These open at their cephalic ends into the 
body cavity, and at their caudal ends, unlike the Wolffian ducts, they unite with one 
another in the middle line. From them are formed in the female—the Fallopian tubes, 
the uterus, and the vagina ; and in the male—the hydatids of the testis or of the epididymis 
and the utriculus prostaticus. 
The Wolffian and Miillerian ducts open at their caudal ends into the ventral or 
