672 DEVELOPMENT OF THE CIRCULATORY APPARATUS. 



tremities, becomes the common iliacs, which in their turn afterward 

 divide into the umbilical arteries proper, and the femorals. Sub- 

 sequently, by the continued growth of the pelvis and lower 

 extremities, the relative size of their vessels is still further in- 

 creased ; and at last the arterial system in this part of the body 

 assumes the arrangement which belongs to the latter periods of 

 gestation. The aorta divides, as before, into the two common iliacs. 

 These also divide into the external iliacs, supplying the lower ex- 

 tremities, and the internal iliacs, supplying the pelvis; and this 

 division is so placed that the umbilical or hypogastric arteries arise 

 from the internal iliacs, of which they now appear to be secondary 

 branches. 



After the birth of the foetus, and the separation of the placenta, 

 the hypogastric arteries become partially atrophied, and are con- 

 verted, in the adult condition, into solid, rounded cords, running 

 upward toward the umbilicus. Their lower portion, however, 

 remains pervious, and gives off arteries supplying the urinary 

 bladder. The obliterated hypogastric arteries, therefore, the rem- 

 nants of the original umbilical or allantoic arteries, run upward 

 from the internal iliacs along the sides of the 

 Fig. 258. urinary bladder, which is the remnant of the ori- 



ginal allantois itself. The terminal continuation 

 of the original abdominal aorta, is the arteria 

 sacra media, which, in the adult, runs downward 

 on the anterior surface of the sacrum, supplying 

 branches to the rectum and the anterior sacral 



nerves. 



Development of the. Venous System. According 

 to the observations of M. Coste, the venous system 

 at first presents the same simplicity and symmetry 

 with the arterial. The principal veins of the 

 body consist of two long venous trunks, the ver- 

 tebral veins (Fig. 258), which run along the sides 

 of the spinal column, parallel with the vertebral 

 arteries. They receive in succession all the inter- 

 Eariy condition of VK- costal veins, and empty into the heart by two 



>ous SYSTEM; show- 1,1 t n -t ,1 t / XT 



ing the vertebral veins lateral trunks of equal size, the canals of Cuvier. 

 emptying into the heart When the inferior extremities become developed, 



hy two lateral trunks, . . . . . . 



the "canals of cuvier." their two veins, returning from below, join the 



vertebral veins near the posterior portion of the 



body ; and, crossing them, afterward unite with each other, thus 



