378 



COMPARATIVE ANATOMY 



becomes connected with the median artery by a volar arch. A fourth 

 vessel, the radialis, grows from the brachial artery into the hand. Dia- 

 grams of these stages (Fig. 317) summarize these changes. 



<^^DIGITAL ART. 



33P32E 



INTEROSSEOUS ART BRACHIAL ARTER^f 



DIGITAL 



1 INTEROS 



SUR BRACHIAL 1 



Median i brachial 



ULNAR 



ischiadic 

 "post tibial 



Fig. 317. — Diagrams of the development of the arteries in arm and leg. A—E, 

 stages in the development of the arteries in the arm; F-I, stages in the development 

 of the arteries of the leg. Proximal is to the right, distal to the left. (From Corning, 

 after McMurrich in Piersol's "Anatomy.") 



ro loA 



Fig. 318. — Three stages in the development of the hepatic portal system. A, 

 primitive; B, liver tubules beginning to develop, right omphalomesenteric interrupted; 

 C, definitive condition, liver not indicated, dc, Cuvierian ducts, hp, hepatic portal 

 vein; hv, hepatic vein; /, liver; lo, ro, left and right omphalomesenteric veins; si, sub- 

 intestinal veins; sv, sinus venosus. (From Kingsley's "Comparative Anatomy of 

 Vertebrates.") 



The arteries of the lower extremity differ somewhat in their develop- 

 ment from those of the upper. Two primary arteries make their appear- 

 ance in the thigh, the femoral and ischiadic arteries. The latter extends 



