GLOSSARY OF EMBRYOLOGICAL TERMS 307 



Urogenital Duct — ducts which open into cloaca of male amphibia and 

 convey both excretory and genital products, derived from mesoneph- 

 ric (Wolffian) ducts. 



Urogenital System — entire excretory and reproductive systems, some em- 

 bryonic parts of which degenerate before hatching. Shows various 

 degrees of common origin and ultimate function. (See specific excretory 

 and reproductive components.) 



Urostyle — fused skeletogenous elements of the last two somites in frog 

 embryo which surround end of notochord as cartilage and finally ossify. 



Utricle— a vesicle, generally referring to superior portion of otocyst which 

 gives rise to the various semi-circular canals of the ear, and into which 

 these canals open. Lined with ectoderm. 



Vasa Deferentia — mesonephric or Wolffian ducts of frog, which persist 

 as male gonoducts of bird and mammal, connecting with testes through 

 vasa efferentia and epididymis and functioning as sperm ducts after 

 degeneration of embryonic mesonephros and development of gonads. 

 (Sing., vas deferens.) 



Vasa Efferentia — ducts which convey frog sperm from collecting tubules 

 through mesorchium to Malpighian corpuscles of mesonephric kidney; 

 derived from rete cords and connected with mesonephric tubules of 

 anterior (sexual) half of the mesonephric or Wolffian body. 



Vegetal Pole — pole of a telolecithal egg where there is greatest concen- 

 tration of yolk, usually opposite animal pole and location of ger- 

 minal vesicle. (Syn., vegetal or vegetative hemisphere; abapical or 

 antipolar hemisphere.) (See Animal Pole.) 



Vein — See under specific names. 



Velar Plate — folds or flaps developing anterior and posterior to branchial 

 regions of frog (anuran) embryo derived from pharyngeal wall and 

 serving as a gross sifting organ between pharynx and gill (branchial) 

 chamber. 



Velum Transversum — depressed roof of telencephalon just anterior to 

 lamina terminalis, which later becomes much folded and vascular as 

 anterior roof of third ventricle. 



Vena Cava Anterior — junction of inferior jugular (anterior cardinal) and 

 subclavian and vertebral veins which empty into ductus Cuvieri, and 

 later the right auricle. (Syn., superior vena cava, superior caval veins.) 



