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AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 



heart. The anterior cardinals persist as the external jugulars; 

 internal jugulars and subclavians are developed later on. So far 

 there is agreement with the Rabbit, but in Man an oblique cross- 

 connection is established between the junction of the left jugular 

 and subclavian and the middle of the right Cuvierian vein. This 

 cross-piece becomes the left innominate vein, the part of the right 

 Cuvierian vein distal to it becomes the right innominate, and the 

 part proximal to it becomes the superior vena cava. The left 

 Cuvierian vein partly aborts, but its proximal end persists as a 

 coronary sinus, which receives the coronary veins and opens into 

 the right auricle, while its distal end becomes the superior inter- 

 costal vein. 



Fig. 105. MAN. Development of Urinogenital Organs (from Landois and 

 Stirling). I, Undiffereiitiated condition D, Gonad, resting on tubules 

 of mesonephros, W; M, Miillerian duct; S, urinogenital sinus. II, 

 Transformations in the female F, Funnel, with hydatid (h'), of 

 Fallopian tube, T; U, utero-vaginal region formed by fusion ; O, ovary, 

 with parovarium, P, &c. Ill, Tranformations in male h, Hydatid of 

 Morgagni ; u, uterus masculinus ; H, spermary (testis), with vasa 

 efferentia running to epididymis, E ; a, vas aberrans ; V, spermiduct 

 (vas deferens). 4, Shows bladder (a) and rectum (d) opening into 

 cloaca. 5, Later stage, where bladder (6) and urinogenital sinus (S) 

 are separated from end of rectum (M) by a perineum (m). 



The posterior cardinals atrophy in the middle of their course ; 

 their hinder ends become the internal iliac veins. The anterior 

 part of the right posterior cardinal is converted into the azygos 



