10G 



GENERAL ANATOMY. 



Between the fourth and fifth Aveek, the inferior vena cava begins to appear 

 in the form of a vessel which passes upwards behind the liver and between the 



Fig. 66. 



B 



Diagram of the formation of the main systemic veins. A. Heart and venous system at the period when 

 there are two venaa cavae superiores, posterior view. 1. Left superior cava. 2. Right superior cava. 3. 

 Inferior cava. 4. Left inferior cardinal. 5. Right inferior cardinal. 6. Right jugular. 7. Anastomosing 

 branch between the jugulars (left innominate). 8. Subclavians. 9. Internal jugular. 10. External jugu- 

 lar. 11. Middle obliterated portion of the posterior cardinal veins. 12. Newly formed posterior vertebral 

 veins. 13. Anastomosis between the two vertebrals trunk of small azygos. 14. Iliac veins, proceeding 

 from anastomosis between the inferior cava and posterior cardinals. 15. Crural. 16. Hypogastric origin- 

 ally the distal ends of the cardinals. B. Heart and permanent vein, posterior view. 1. Obliterated left 

 superior cava. 6. Right innominate. 7. Left innominate. 8. Subclavian. 10. Jugular. 13. Trunk of 

 the small azygos. 17. Coronary sinus receiving the coronary vein. 18. Superior intercostal. 19. Superior 

 email azygos. 20. Inferior small azygos. 



two Wolffian bodies. It anastomoses below with the two cardinal veins, and 

 with the crural veins, which gradually come to open into it. 



The middle part of the cardinal veins disappears ; their distal extremities 

 persist as the hypogastric veins, which open along with the crural into the 

 vena cava, forming the iliac and other veins of the lower extremities. The 

 termination of each cardinal vein above, in the sinus of Cuvier, or superior 

 cava, also persists. The central atrophied portion of the cardinal veins is re- 

 placed by a vein on either side, called posterior vertebral, which receive the 

 intercostal and lumbar veins, and are soon united by an oblique anastomosing 

 branch. The right vertebral vein, together with the persistent termination of 

 the right cardinal vein, forms the great azygos vein. The distal portion of the 

 left vertebral vein with the oblique anastomosing branch, forms the small 

 azygos ; and the upper part of the left vertebral, with the persistent termina- 

 tion of the left cardinal, forms the left superior intercostal vein. 



The Foetal Circulation is spoken of in the body of the work, under the 

 subject of the Thorax. 



Development of the Alimentary Canal. The development of the intestinal 

 cavity is, as shown above, p. 97, one of the earliest phenomena of embryonic 

 life. This original intestine is closed at either end, and is at first in free com- 

 munication with the umbilical vesicle (Fig. 59, 3). It is divided into three 

 toarts : the anterior or cephalic portion of the primitive intestine ; the middle, 



