THE . DEVELOPMENT OF THE UROGENITAL SYSTEM. 



421 



the mesonephros leaves a few tubules which come to lie near the head of the epi- 

 didymis and form the paradidymis (or organ of Giraldes) , the tubules of which 

 are lined with columnar, ciliated epithelium. Near the transition from the 

 duct of' the epididymis to the deferent duct there is almost invariably a tubule 

 (sometimes branched) which also represents a remnant of the mesonephros and 

 is known as the aberrant ductule. It usually opens into the duct of the epididy- 

 mis, but may lie free in the tissue around it (Fig. 347). 



Atrophy of the Mullerian Ducts. — These ducts persist in the female 

 and become the oviducts, uterus and vagina; in the male they degenerate and 

 disappear almost entirely. The degeneration begins about the time they open 



Diaphragmatic 

 gg ligament of 

 ^ mesonephros 



Genital gland 



Mesonephros 



Mesonephric duct 



Urachus 



Umbilical artery 



Mesonephric duct 



Inguinal ligament 



Fig. 374. — Urogenital organs in a human embryo of 17 mm. (6 weeks). Kallmann's Atlas. 



into the urogenital sinus (embryos of 25 to 28 mm.) ; by the time the embryo 

 reaches a length of 60 mm. only the extreme cephalic end and the caudal 

 third remain, and at 90 mm. the entire duct is gone except the extreme ends. 

 The cephalic end persists as the appendix testis (or hydatid of Morgagni) 

 (Figs. 347, 379). The caudal end persists as the utriculus prostaticus (uterus 

 masculinus) . 



Changes in the Positions of the Genital Glands and the Development 



of their Ligaments. 



During the early stages of development the genital glands— testicles or 

 ovaries— are situated far forward in the abdominal cavity. During the eighth 

 week they lie opposite the lumbar vertebra. During the succeeding months, 

 up to the time of birth, they gradually move caudally to the positions they 



