EXPLANATION OF PLATES. XX111 



sinus, a, a, a. The blood returns from this by two superior branches, b, 6, and 

 two inferior, c, c, of the omphalo-raeseraic veins, to the heart, d; which , at 

 this period, a tube curved on itself, and presenting the first indication of a 

 division into cavities. The two aortic trunks appear, in the abnormal region, 

 as the inferior vertebral arteries, e, e; from which are given off the omphalo- 

 meseraic arteries, /,/, which form a net-work that distributes the blood over 

 the vascular area. In the cephalic region is seen the anterior cerebral vesi- 

 cles, with the two ocular vesicles, g. After Bischoff ( 762). 



